Eight Sleep is a temperature-controlled mattress cover that circulates water through a thin layer on top of your bed, cooling or heating each side independently between 55°F and 110°F. It also tracks your sleep using sensors embedded in the cover, then uses that data to automatically adjust the temperature throughout the night. Here’s how each piece of the system actually works.
The Active Grid and Hub
The core of Eight Sleep is a thin cover (called the Pod) that sits on top of your existing mattress. Inside the cover is a network of small tubes, referred to as the “Active Grid.” Water flows through these tubes, and the temperature of that water is what makes your bed feel cool or warm.
The cover connects to a bedside unit called the Hub, which is essentially a water reservoir with a heating and cooling system built in. The Hub pulls water from the grid, adjusts its temperature, and pumps it back through. You can set the temperature in single-degree increments anywhere from 55°F to 110°F, and each side of the bed operates independently. So if you sleep hot and your partner sleeps cold, you can each set your own temperature without compromise.
The Hub does produce some noise during operation. User measurements put it around 35 to 39 decibels, roughly comparable to a quiet whisper or a soft refrigerator hum. Most people adjust to it quickly, though placement matters. Keeping the Hub a few feet from your head rather than right next to your pillow makes a noticeable difference.
How the Sensors Track Your Sleep
Built into the mattress cover are piezoelectric sensors that detect tiny changes in pressure. These sensors pick up the subtle vibrations your body creates as you breathe and as your heart beats, which allows the system to estimate several biometrics without you wearing anything on your wrist or finger:
- Heart rate and heart rate variability (HRV)
- Respiratory rate
- Sleep stages (light, deep, and REM)
- Sleep position and movement
- Sleep disturbances
Because the sensors are embedded in the surface you’re lying on, they collect data passively all night. There’s nothing to charge, nothing to forget to put on, and no wristband leaving marks on your skin. The tradeoff is that body-contact sensors like these are generally less precise than medical-grade chest straps, but for night-to-night trend tracking, they’re consistent enough to reveal meaningful patterns.
Autopilot: Automatic Temperature Adjustments
Eight Sleep’s most distinctive software feature is called Autopilot. Rather than setting a single temperature for the whole night, Autopilot adjusts the bed’s temperature dynamically as you sleep, responding to what’s actually happening with your body and your environment.
The system builds a profile of you as a sleeper over time. It factors in your biometric data (heart rate, HRV, respiratory rate, sleep stages), your historical sleep patterns, and even real-time local weather. On a hot summer night, for example, Autopilot might cool the bed more aggressively than it would during a mild spring evening. If you tend to wake up at 3 a.m. because your body temperature rises during REM sleep, it can learn that pattern and pre-cool the bed before it happens.
As any of these factors change, the algorithm adapts. A stressful week with elevated heart rates, a cold front moving through your city, a shift in your sleep schedule: Autopilot accounts for all of it and recalibrates. The goal is to keep your skin temperature in the range most conducive to staying asleep, without you ever opening the app.
What the Research Shows
A study published on ResearchGate examined sleep quality changes after one month of using the Pod. Before using it, participants took an average of 28 minutes to fall asleep. After a month, that dropped by 44%, a reduction of about 12 minutes. Sleep disturbances decreased by 23% overall, with heat-related disturbances specifically dropping by 69%. All of these improvements were statistically significant.
These results make intuitive sense. Your core body temperature needs to drop by about one to two degrees for sleep to initiate, and temperature disruptions are one of the most common reasons people wake up during the night. A system that actively manages bed temperature addresses both problems directly.
What You Get Without a Subscription
Eight Sleep works out of the box for its core functions, but several features require a monthly membership. Here’s how the split breaks down.
Without a subscription, you get dual-zone cooling and heating, the ability to schedule temperature changes throughout the night, and basic sleep tracking including sleep stages, heart rate, and respiratory rate. That covers the fundamental value of the product: a bed that stays the temperature you want it to be.
The subscription unlocks Autopilot (automatic temperature adjustments), advanced sleep insights and long-term trend analysis, the vibration and thermal alarm that wakes you with gentle temperature changes instead of sound, detailed health reports flagging unusual metrics, and ongoing software updates with new features. If you want the system to learn and adapt on its own rather than relying on manual schedules, the subscription is where that intelligence lives.
Setup and Maintenance
The Pod cover fits over your existing mattress, similar to a fitted sheet but thicker. You connect the cover’s tubing to the Hub, fill the Hub’s reservoir with water, and pair everything through the Eight Sleep app. The entire setup takes most people around 30 minutes.
For ongoing maintenance, you’ll need to refill the water reservoir periodically as some water evaporates over time. Eight Sleep previously recommended using distilled water with hydrogen peroxide to prevent microbial growth inside the tubing, but the company has since updated its guidance. Internal testing showed those additives aren’t necessary, and current instructions simply call for tap water. Some users still add a small amount of hydrogen peroxide for peace of mind, and Eight Sleep has confirmed there’s no downside to doing so.
The cover itself is removable and machine washable, which helps with general hygiene. The Hub should be kept in a spot with decent airflow so it can dissipate heat efficiently during cooling cycles.
How Each Side Stays Independent
One of the most practical features for couples is true dual-zone control. The Active Grid is split down the middle of the bed, and each half has its own water circuit. Your side might be set to 65°F while your partner’s side runs at 85°F, and there’s minimal bleed between the two zones. Each person controls their side through the app, sets their own schedule, and gets their own sleep data and biometric reports. Autopilot also runs independently for each sleeper, building separate profiles and making separate adjustments throughout the night.