An Experiment: How Couples Affect Each Other's Sleep

by Jesse Menayan

Jun 25, 2018

Jesse Menayan is a design director at Casper and holds patents ranging from bikes to furniture, all products that touch the body.

In our efforts to create an even more comfortable night of sleep, it’s imperative that we study the relationship between our products, the humans snuggling on and under them, and the environment in the house around them, because it’s something we can influence through design and engineering.

We’re on a never ending quest to create an even more comfortable sleep experience for people. A colleague of mine, who we’ll identify as “Betty,” approached me a while ago and claimed that her boyfriend, “Freddy,” was a sweaty sleeper who was always stealing the sheets. She asked if we could help them settle the debate. We were already running similar tests with participants in California—measuring how temperature and humidity influence people’s sleep—so I was happy to. What we found shows just how active our nights really are.

First, we had to set up the experiment. Past research shows that each person, to a degree, sleeps in a micro-climate that’s unique to them. My teammate, Jordan Lay, had already designed custom sleep sensors that measure temperature and humidity, so I had Betty and Freddy wear a set of them. We gathered a week’s worth of data on how they slept and Duncan, a data analyst and colleague, looked for clues in the numbers. A picture of night life (the sleepy kind) came to life.

differences in partner sleep graph illo

We dug into temperature first. Even though Betty was certain that Freddy slept hotter, we didn’t find a significant difference in temperature between the two. Over multiple nights, Freddy slept only a little warmer than Betty. The temperature of the air directly surrounding Freddy was an average of 33 degrees celcius. Betty’s was 32 degrees. A similar result.

However, the humidity levels in the air around Freddy were very different. While the temperature was only a couple degrees difference, Freddy gave off A LOT more moisture, even though they were both wearing similar-weight pyjamas. The relative humidity around Freddy was an average of 57%, compared to Betty at 46%. His also fluctuated significantly throughout the night. Freddy’s standard deviation was +/- 10 percentage points during the night. Betty’s was +/- 3 percentage points. Here it’s hard to believe that they are sleeping in the same bed.

The two definitely impacted each other’s environment too. When we dug into the numbers, we saw significant spikes and dips in each person’s sleep environment that appear to be directly related to the other’s. Here is an example of one night, below. The blue lines call out points where we believe Freddy “stole the covers”—and got more humid—while Betty lost them and got less humid.

movement graph

Betty was super fascinated by the data. The first time I shared the info, she went “AHAA!!!!”. Here was final, compelling proof that Freddy was a sweaty sleeper (and a sheet-stealer), and it had an impact on her sleep. I’m sure Freddy enjoyed hearing all about it.

For us, as designers and engineers, we’ve been incorporating our research into temperature, humidity, and comfort into the products we design. A lot of sheets are really dense, so we engineered the Casper sheets to support positive airflow. Colleagues of mine chose a unique weave for the Casper pillow that helps heads stay cool during the night, and we also designed our mattress so it doesn’t trap heat beneath the body. Integrating our research into each product we create is part of what’s exciting about being at a sleep company like Casper. Now we just need to get a full sleep system to Betty and Freddy.

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