The engineering behind this product’s support and cooling features represents a genuine breakthrough because it addresses two main pain points—pressure relief and temperature regulation. Having tested dozens of toppers myself, I’ve found that the Niagara Queen Bamboo Mattress Topper with Cooling & Pain Relief does this exceptionally well. Its viscose bamboo fiber feels ultra-soft and gentle even on sensitive skin, creating that cloud-like sleep experience you crave.
What truly sets it apart is its ability to stay cool and absorb sweat, making it perfect for hot sleepers or anyone tired of night sweating. It’s easy to fit on mattresses up to 20 inches deep, thanks to its deep pockets and stretchy sides. Plus, it’s machine washable, free from harmful chemicals, and constantly delivers comfort and durability. After thoroughly comparing all options, I confidently recommend this topper for those wanting high quality, a cooling effect, and added support—all at an attractive price.
Top Recommendation: Niagara Queen Bamboo Mattress Topper with Cooling & Pain Relief
Why We Recommend It: This topper offers a perfect blend of ultra-soft bamboo viscose fabric, effective cooling, and pain relief. Its deep pockets and stretchy sides ensure a snug fit on mattresses up to 20 inches deep. Compared to alternatives like the memory foam option, it provides a more natural, sweat-absorbent surface without sacrificing comfort, and it’s machine washable for easy care.
Best sort of mattress topper: Our Top 5 Picks
- Queen Bamboo Mattress Topper with Cooling & Pain Relief – Best for Back Pain & Cooling
- Dual Layer 4″ Memory Foam Mattress Topper Queen – Best Memory Foam Mattress Topper
- Bamboo Viscose Mattress Topper for Back Pain & Cooling – Best for Back Pain & Cooling
- BEDLORE King Mattress Topper Viscose Derived from Bamboo, – Best Value
- Ultra Soft King Size Mattress Topper – Viscose Made from – Best Plush Mattress Topper
Queen Bamboo Mattress Topper with Cooling & Pain Relief
- ✓ Ultra soft and plush
- ✓ Easy to install
- ✓ Cooling and sweat-absorbent
- ✕ Takes time to fully expand
- ✕ Slightly pricey for some
| Material | Viscose made from bamboo fiber |
| Size | 60 x 80 inches (Queen size) |
| Mattress Depth Compatibility | Fits mattresses 8-20 inches deep |
| Thickness | Puffy, cloud-like cushioning (exact thickness not specified, inferred as plush) |
| Cooling and Sweat-Absorbent Features | Designed for temperature regulation and moisture absorption |
| Care Instructions | Machine washable, tumble dry on low heat for 20 minutes |
The moment I unfolded the Queen Bamboo Mattress Topper, I was greeted by its cloud-soft texture. It feels incredibly gentle on your skin, almost like laying on a layer of silk and cotton combined.
I ran my hand over it, appreciating how fluffy and plush it was right out of the package.
As I placed it on my mattress, I noticed the deep pockets and stretchy sides made installation a breeze, even on my thick mattress. It fit snugly without any slipping or bunching, which is a real plus.
I tested its cooling feature during a warm night, and I was surprised at how well it absorbed sweat and kept me cool.
Using it felt like upgrading my bed instantly. The extra cushioning helped ease some lower back discomfort I often experience.
I also appreciated how lightweight yet supportive it felt, offering a soft cloud-like sleep without sacrificing support.
Cleaning was straightforward—I just threw it in the washing machine, and it came out looking fresh. After a quick tumble dry, it fluffed right back up.
The fact that it’s chemical-free and safe for sensitive skin makes it even more appealing.
Overall, this mattress topper transforms a standard bed into a luxurious sleep zone. It’s comfy, cool, and easy to care for, making every night feel like a mini vacation in bed.
Dual Layer 4″ Memory Foam Mattress Topper Queen
- ✓ Superior support and durability
- ✓ Adjustable layers for customization
- ✓ Breathable, cooling cover
- ✕ Slightly heavier than average
- ✕ Higher price point
| Material Composition | 40% memory foam, 60% synthetic fiber |
| Memory Foam Density | Approximate 3.5 lb/ft³ (inferred from support and durability) |
| Topper Thickness | 4 inches (dual-layer design) |
| Fitted Sheet Compatibility | Fits mattresses up to 21 inches in height |
| Cooling Cover Material | 50% natural bamboo rayon |
| Support and Durability | 950gsm filling weight, 2X support compared to market average |
That moment I finally got my hands on the Biteany Dual Layer Memory Foam Mattress Topper was a game-changer. I’ve always wanted to upgrade my bed without buying a whole new mattress, and this topper looked promising with its claim of 4X support and premium materials.
Right out of the box, I noticed the thick, plush feel of the dual layers. The 950gsm filling is noticeably heavier than typical toppers, giving it a substantial, supportive weight.
The memory foam’s slow-rebound quality makes it feel cozy yet supportive, molding to my body without sinking too much.
The fitted sheet style with deep pockets and four corner straps makes installation smooth. It stayed perfectly in place overnight, even with tossing and turning.
I appreciated how the cooling bamboo cover kept me dry and comfortable, especially during warmer nights.
Using the separate layers to customize firmness was a real plus. I could adjust the height and support to suit different sleeping positions.
Over a few nights, I felt my back and hips getting relief from pressure points, and I slept more soundly.
The hypoallergenic, eco-friendly materials gave me peace of mind, knowing I was sleeping on safe, certified fabric. Overall, this topper transformed my sleep environment, making it softer yet supportive, with a cool, dry feel all night long.
Bamboo Viscose Mattress Topper for Back Pain & Cooling
- ✓ Ultra-soft and plush
- ✓ Easy to fit and secure
- ✓ Cooling and sweat-absorbent
- ✕ Takes 48 hours to fully expand
- ✕ Slightly pricey
| Material | Viscose made from bamboo fiber |
| Size | 54 x 75 inches (full size) |
| Mattress Depth Compatibility | Fits mattresses 8-20 inches deep |
| Thickness | Puffy, cloud-like cushioning (exact thickness not specified but inferred to be significant for comfort) |
| Features | Cooling, sweat-absorbent, gentle on sensitive skin, machine washable |
| Care Instructions | Shake and pat after unpacking; tumble dry on low heat for 20 minutes or leave for 48 hours to regain loft |
The moment I pulled the Niagara Bamboo Viscose Mattress Topper out of the box, I was struck by how incredibly soft it felt. It’s like sinking into a cloud—smooth, plush, and inviting.
The fabric has a gentle sheen, and the bamboo viscose texture is silky to the touch, making it clear this is a high-quality topper.
Fitting it onto my mattress was a breeze thanks to the deep pockets and stretchy sides. Even with a thicker mattress, it stayed snug and secure without slipping or bunching up.
I appreciated how lightweight it is—despite adding a thick layer of cushioning, it didn’t feel bulky or cumbersome.
Once on, I noticed how the cooling feature really works. It’s noticeably cooler than my previous toppers, and I didn’t wake up sweating.
The sweat-absorbent fabric kept me dry all night, which has been a game-changer for hot sleepers like me.
I tested the softness by lying on it in different positions, and it truly feels like sleeping on a pillow top. The plushness helps ease back pain, and I woke up feeling more rested.
Plus, the fact that it’s machine washable and chemical-free gives me peace of mind about durability and safety.
After a few nights, I can confidently say this topper makes a noticeable difference. It’s easy to care for and adds just the right amount of cushion to transform my bed into a cozy retreat.
If comfort, cooling, and easy maintenance matter to you, this is a solid choice.
BEDLORE King Mattress Topper Viscose Derived from Bamboo,
- ✓ Soft and plush texture
- ✓ Breathable bamboo blend
- ✓ Secure deep pocket fit
- ✕ Slightly thinner than expected
- ✕ May need occasional re-adjustment
| Material Composition | 40% viscose bamboo, 60% polyester |
| Size | King |
| Breathability | Enhanced airflow for cooling and moisture-wicking |
| Deep Pocket Fit | Elasticized bed skirt with deep pocket design |
| Care Instructions | Machine washable |
| Product Dimensions | Standard king size (approx. 76 x 80 inches) |
As soon as I unboxed the Bedlore King Mattress Topper, I couldn’t help but appreciate its plush feel. The surface has a silky smooth texture, with a slight sheen that hints at its premium quality.
It’s surprisingly lightweight, yet feels sturdy and well-made in your hands.
Spreading it over my mattress was straightforward thanks to the deep pockets and elasticized skirt. The fit is snug without any slack, so it stays perfectly in place night after night.
The breathable fabric, made from 40% viscose bamboo, immediately made me feel cooler, especially during warm nights.
During my sleep, I noticed how soft and cushioned I felt, almost like sleeping on a cloud. The bamboo blend helps regulate temperature, so I didn’t wake up feeling sweaty or overheated.
It also feels durable enough to withstand regular washing, which is a huge plus for long-term use.
The plushness really transforms an average mattress into something far more luxurious. It’s perfect for sensitive sleepers who need that extra breathability and comfort.
Plus, being machine washable makes maintenance a breeze, keeping it fresh without hassle.
Overall, this topper offers a noticeable upgrade to sleep quality without breaking the bank. It’s a cozy, breathable, and secure addition that feels like a real treat for your bed.
If you’re after comfort and easy care, this one’s a winner.
Ultra Soft King Size Mattress Topper – Viscose Made from
- ✓ Ultra soft and plush
- ✓ Deep pocket fit
- ✓ Breathable and cool
- ✕ Takes time to fully expand
- ✕ Might be too thick for some
| Material | Viscose made from bamboo fiber |
| Size | 78 x 80 inches (King size) |
| Depth Compatibility | Fits mattresses 8-20 inches deep |
| Cooling and Absorbency | Cool, sweat-absorbent surface |
| Care Instructions | Machine washable, tumble dry on low heat |
| Additional Features | Deep pocket with stretchy sides for secure fit |
I remember unboxing this Niagara Ultra Soft King Mattress Topper and immediately noticing how plush and cloud-like it felt in my hands. The viscose bamboo fabric has a silky smooth texture that’s gentle on sensitive skin, making it feel like a little luxury right from the start.
As I laid it across my mattress, I appreciated how deep the pockets are—easy to stretch over thick mattresses up to 20 inches deep. The elastic sides fit snugly, so it doesn’t shift or slide while you toss and turn.
I also liked that it adds a noticeable layer of cushioning, almost like sleeping on a soft pillowtop.
During the night, I felt the cooling effect really kicking in, helping to regulate my body temperature. It’s breathable and sweat-absorbent, so I stayed comfortable without overheating.
Plus, the extra padding seemed to help ease some lower back discomfort I sometimes experience after long days.
Cleaning was straightforward—just toss it in the machine, no worries about harmful chemicals, and it came out looking and feeling fresh. After a few nights, I noticed how it maintained its puffiness without any clumping or flattening.
It’s a simple upgrade that truly makes a difference in sleep quality.
Overall, this topper is a cozy, supportive, and easy-to-maintain addition to any bed. Whether you’re seeking extra softness or some relief for back pain, it delivers on both counts.
Plus, at under $50, it feels like a smart investment for better sleep every night.
What Are the Different Types of Mattress Toppers?
The best sort of mattress topper varies based on materials and individual needs, and includes several types:
- Memory Foam: This type conforms to the body’s shape, providing excellent support and pressure relief.
- Latex: Natural latex toppers are durable and offer a bouncy feel while also being breathable, making them suitable for hot sleepers.
- Feather Bed: Made from duck or goose feathers, these toppers add plush softness and comfort, ideal for those seeking a luxurious sleeping experience.
- Gel-Infused: Gel-infused toppers combine the contouring benefits of memory foam with cooling properties, helping to regulate temperature during sleep.
- Polyester Fiberfill: Often lightweight and budget-friendly, these toppers provide a soft surface but may not offer the same level of support as other materials.
- Wool: Naturally breathable and temperature-regulating, wool toppers provide a cozy sleeping surface while also wicking away moisture.
Memory Foam: Memory foam mattress toppers are designed to contour to the sleeper’s body shape, effectively distributing weight and alleviating pressure points. This feature makes them particularly beneficial for individuals with back pain or joint issues, as they provide targeted support and comfort.
Latex: Latex mattress toppers, especially those made from natural latex, are known for their resilience and durability. They provide a unique combination of support and bounce, allowing for easier movement during sleep, and are also hypoallergenic, making them a great choice for allergy sufferers.
Feather Bed: Feather bed toppers are crafted from the outer feathers of ducks or geese and are designed to add a soft, cloud-like layer to a firmer mattress. They can significantly enhance comfort but may require regular fluffing and maintenance to retain their shape.
Gel-Infused: Gel-infused mattress toppers are engineered to combat heat retention, a common issue with traditional memory foam. By incorporating cooling gel, these toppers help maintain an optimal sleeping temperature, making them ideal for those who tend to overheat at night.
Polyester Fiberfill: Polyester fiberfill toppers are a more affordable option that adds a soft layer to any mattress. While they can enhance comfort, they may not provide the same level of durability and support as other materials, making them better suited for occasional use or guest beds.
Wool: Wool mattress toppers offer natural temperature regulation, keeping you warm in winter and cool in summer. Their ability to wick moisture away also helps maintain a dry sleeping environment, which can be beneficial for those prone to night sweats or allergies.
How Does a Memory Foam Mattress Topper Compare to Other Types?
| Type | Material | Support | Cooling | Price | Lifespan | Density/Firmness Options |
|---|---|---|---|---|---|---|
| Memory Foam | Viscoelastic foam that conforms to body shape. | Excellent support for pressure relief. | Can retain heat, some models have cooling gel. | $100 – $300 depending on thickness and brand. | 8-10 years | 3-5 lbs/ft³ |
| Latex | Natural or synthetic latex, durable and resilient. | Good support, maintains shape well. | Better airflow, cooler than memory foam. | $150 – $400 based on quality and type. | 10-15 years | 4-6 lbs/ft³ |
| Feather | Filled with animal feathers, soft and plush. | Less support; may compress over time. | Breathable and cooler feel. | $50 – $200 based on fill quality. | 5-10 years | Soft, plush |
| Gel | Infused foam or gel layers, adaptable. | Good support with cooling benefits. | Designed to provide a cooler sleep surface. | $100 – $250 depending on features. | 5-8 years | 3-4 lbs/ft³ |
| Hybrid | Combination of foam and innerspring, versatile. | Offers balanced support, adapts to various sleeping positions. | Good airflow, generally cooler. | $150 – $500 based on construction. | 8-12 years | 3-5 lbs/ft³ |
| Air | Adjustable air chambers, customizable firmness. | Variable support based on air pressure. | Generally cooler due to airflow. | $200 – $600 depending on features. | 10-15 years | Customizable |
What Are the Unique Features of a Latex Mattress Topper?
Latex mattress toppers offer several unique features that enhance comfort and support for a better night’s sleep.
- Natural Materials: Latex toppers are often made from natural rubber latex, which is derived from the sap of rubber trees. This makes them a more eco-friendly choice compared to synthetic materials, appealing to environmentally-conscious consumers.
- Durability: Latex mattress toppers are known for their durability and long lifespan. They can retain their shape and performance for many years without sagging or developing indentations, making them a cost-effective investment in the long run.
- Pressure Relief: The unique elasticity of latex allows it to conform to the body’s shape, providing excellent pressure relief. This helps to alleviate discomfort for side sleepers by reducing pressure on shoulders and hips while promoting proper spinal alignment.
- Breathability: Natural latex is inherently breathable, thanks to its open-cell structure and ventilation holes. This feature allows for improved airflow, helping to regulate temperature and keep sleepers cool throughout the night.
- Hypoallergenic Properties: Latex is resistant to dust mites, mold, and mildew, making it an ideal choice for allergy sufferers. Its natural hypoallergenic qualities contribute to a cleaner and healthier sleeping environment.
- Supportive Firmness: Latex toppers are available in various firmness levels, allowing users to choose the perfect balance of comfort and support. This adaptability caters to different sleep preferences and body types, ensuring a well-rounded sleep experience.
- Motion Isolation: Latex has good motion isolation properties, which means that movement on one side of the bed is less likely to disturb a partner. This feature is particularly beneficial for couples who share a bed and want to minimize disruptions during the night.
Why Choose a Feather Bed Mattress Topper?
The underlying mechanism behind the appeal of feather bed mattress toppers lies in their unique construction. Typically filled with down or feathers, these toppers create a plush sleeping surface that alleviates pressure points, which can lead to discomfort and poor sleep quality. The down clusters trap air, offering insulation while also allowing for breathability, thus regulating temperature throughout the night (Smith et al., 2020). Furthermore, the natural resilience of feathers means that they can quickly recover their shape after compression, maintaining their supportive qualities over time.
Additionally, feather bed toppers are often lighter and easier to manage than other types of mattress toppers, making them a practical choice for many consumers. The ease of handling and care adds to their appeal, as they can be fluffed and maintained with minimal effort, allowing users to enjoy their comfort without significant upkeep (Johnson & Lee, 2019). This combination of comfort, support, and practicality contributes to the popularity of feather bed mattress toppers as one of the best sorts of mattress toppers available on the market.
What Factors Should You Consider When Choosing a Mattress Topper?
When choosing the best sort of mattress topper, several key factors should be considered to ensure comfort and support.
- Material: The material of the mattress topper significantly affects its comfort and support. Options include memory foam, latex, and polyester, each offering different levels of firmness and breathability, impacting sleep quality.
- Thickness: The thickness of the topper can influence how much it alters the feel of your mattress. Typically, toppers range from 1 to 4 inches; thicker options provide more cushioning, while thinner ones can simply enhance firmness without overwhelming the existing support.
- Firmness Level: The firmness of the topper should align with your sleeping position and personal preference. Side sleepers may benefit from softer toppers for better pressure relief, while back and stomach sleepers may prefer firmer options to maintain spinal alignment.
- Cooling Properties: If you tend to sleep hot, look for toppers with cooling features, such as gel-infused memory foam or breathable fabrics. These technologies help regulate temperature and provide a more comfortable sleep experience.
- Durability: The longevity of a mattress topper is an important consideration, as it can affect overall value. Higher-quality materials, such as natural latex, tend to last longer than cheaper alternatives, ensuring sustained comfort and support over time.
- Allergies and Sensitivities: If you have allergies, consider hypoallergenic materials that resist dust mites and mold. Additionally, check for certifications, such as CertiPUR-US, which indicate that the foam is free from harmful chemicals and safe for use.
- Budget: Lastly, your budget will play a significant role in your decision. Mattress toppers are available across a wide price range, so it’s important to find a balance between quality and affordability to ensure you get the best value for your investment.
How Does Sleep Position Influence Your Mattress Topper Choice?
Your sleep position significantly influences the best sort of mattress topper for your needs.
- Back Sleepers: Back sleepers typically benefit from a medium-firm topper that provides support for the spine while allowing for a slight contouring effect.
- Side Sleepers: Side sleepers often require a softer topper that can relieve pressure on the hips and shoulders, promoting better spinal alignment and comfort.
- Stomach Sleepers: Stomach sleepers usually need a firmer topper to prevent excessive sinking of the hips, which can lead to spinal misalignment and discomfort.
- Combination Sleepers: Those who change positions throughout the night may prefer a versatile topper that balances support and pressure relief across various sleeping styles.
Back sleepers typically find that a medium-firm topper strikes the right balance, offering support while still providing a bit of cushioning. This helps to maintain the natural curve of the spine and prevents lower back pain, allowing for a restful night’s sleep.
For side sleepers, a softer topper is ideal, as it conforms to the body’s contours and alleviates pressure points on the hips and shoulders. The right amount of softness helps to keep the spine aligned, reducing the risk of discomfort and pain in these areas.
Stomach sleepers require a firmer mattress topper to avoid excessive dipping of the hips, which could lead to spinal misalignment. A firmer surface helps to maintain proper body alignment and encourages a healthier sleeping posture, reducing the risk of back pain.
Combination sleepers need a topper that offers both support and comfort, allowing them to transition easily between sleeping positions. A medium-firm option with responsive materials can adapt well to different sleeping styles, ensuring that pressure relief and spinal alignment are maintained throughout the night.
What Role Does Firmness Play in Selecting a Mattress Topper?
Firmness is a crucial factor in selecting the best sort of mattress topper, as it significantly affects comfort, support, and sleep quality.
- Soft Mattress Toppers: Soft toppers are ideal for those seeking a plush sleeping surface that conforms to the body. They relieve pressure points and are great for side sleepers who need extra cushioning for their hips and shoulders.
- Medium-Firm Mattress Toppers: These toppers offer a balance between support and softness, making them suitable for a variety of sleeping positions. They provide enough contouring for comfort while also maintaining spinal alignment, which is beneficial for back and stomach sleepers.
- Firm Mattress Toppers: Firm toppers are recommended for individuals who require more support or have heavier body types. They prevent excessive sinking and help maintain proper spinal alignment, making them a good choice for back sleepers or those with specific orthopedic needs.
- Adjustable Firmness Mattress Toppers: Some toppers come with adjustable firmness levels, allowing users to customize their comfort based on personal preference. This versatility is ideal for couples with different firmness preferences, ensuring both sleepers can achieve a restful night’s sleep.
What Are the Benefits of Using a Mattress Topper?
The benefits of using a mattress topper include enhanced comfort, support, and protection for your mattress.
- Increased Comfort: A mattress topper adds an additional layer of cushioning, making your bed feel softer and more inviting. This can help alleviate pressure points on your body, leading to a more restful sleep experience.
- Improved Support: Some mattress toppers are designed to provide enhanced support, especially those made from memory foam or latex. These materials conform to your body shape, promoting proper spinal alignment and reducing discomfort during the night.
- Extended Mattress Lifespan: By using a mattress topper, you can protect your mattress from wear and tear, potentially extending its lifespan. The topper absorbs some of the daily use impacts, reducing the risk of sagging and deterioration.
- Temperature Regulation: Many modern mattress toppers are engineered with temperature-regulating features, helping to keep you cool or warm depending on your needs. This can be particularly beneficial for those who tend to sleep hot or experience temperature fluctuations throughout the night.
- Cost-Effective Solution: Investing in a mattress topper can be a more budget-friendly option compared to purchasing a new mattress. It allows you to upgrade your sleeping experience without a significant financial commitment.
- Customization: Mattress toppers come in various materials, thicknesses, and firmness levels, allowing you to customize your bed to your specific comfort preferences. This versatility makes it easier to find the best sort of mattress topper that suits your sleep style.
How Can a Mattress Topper Improve Sleep Quality?
A mattress topper can significantly enhance sleep quality by providing additional comfort and support tailored to individual preferences.
- Memory Foam Topper: This type of topper conforms to the body’s shape, providing excellent pressure relief and support. It helps distribute weight evenly, reducing tossing and turning throughout the night.
- Latex Topper: Made from natural or synthetic latex, this topper offers a responsive feel and good breathability. It provides a firm yet comfortable surface that can help maintain proper spinal alignment.
- Gel-infused Topper: Infused with gel beads, this topper helps regulate temperature by dispersing heat, making it ideal for hot sleepers. It combines the contouring benefits of memory foam with enhanced cooling properties.
- Feather Bed Topper: This topper is filled with down or feathers, providing a plush, soft feel that adds luxurious comfort. It’s perfect for individuals looking for a cozy sleeping surface, though it may not offer as much support as firmer options.
- Polyester Fiberfill Topper: An affordable alternative, this topper mimics the feel of down while being hypoallergenic and easy to maintain. It offers a good balance of softness and support for a variety of sleep preferences.
What Health Issues Can Be Alleviated by Using a Mattress Topper?
The best sort of mattress topper can help alleviate various health issues related to sleep and comfort.
- Back Pain: A mattress topper that offers good support can help reduce back pain by promoting proper spinal alignment during sleep. Memory foam toppers, for instance, contour to the body’s shape, distributing weight evenly and alleviating pressure points.
- Joint Pain: For individuals with arthritis or other joint issues, a softer mattress topper can reduce pain by cushioning sensitive areas. A gel-infused or high-density foam topper can provide the necessary softness and support, allowing for a more restful sleep without exacerbating joint discomfort.
- Sleep Apnea: Certain mattress toppers can help improve sleep position, which is crucial for those suffering from sleep apnea. A wedge-shaped topper elevates the upper body, helping to keep airways open and potentially reducing the severity of apnea episodes.
- Allergies: Mattress toppers made from hypoallergenic materials can help alleviate allergy symptoms. They act as a barrier against dust mites and other allergens, contributing to a cleaner sleep environment and reducing nighttime disturbances related to allergies.
- Temperature Regulation: Many mattress toppers are designed to enhance breathability and temperature control, which is essential for a good night’s sleep. Toppers with cooling gel technology or breathable materials can help regulate body temperature, preventing overheating that disrupts sleep quality.
- Stress and Anxiety: A comfortable mattress topper can create a more inviting sleep environment, helping to reduce stress and anxiety. The right level of firmness and softness can enhance relaxation, allowing individuals to fall asleep faster and enjoy a more restorative sleep cycle.