What We Learned From an Experiment on How Couples Affect Each Other’s Sleep


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 with 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 learn more about the sleep environment and create an even better one for people. A colleague of mine, who we’ll identify as “Betty,” approached me a while ago and asked if we could help her figure out if her boyfriend, “Freddy,” was as sweaty of a sleeper as she thought. We were already running similar tests with participants in California—measuring how the environment changes around them throughout the night so it can guide our design decisions—and I was happy to help them learn more about how they sleep. What we found is that Freddy certainly was a “sweaty sleeper,” and his movements during the night significantly impacted Betty’s sleep environment.

The data on how this one couple sleeps is fascinating. Past research shows that each partner, to a degree, sleeps in a climate that is unique to them. I gave Betty and Freddy a set of our sleep sensors that measure temperature and relative humidity at one-minute intervals. They wore them for a week. I worked with Duncan, a colleague of mine in New York and data analyst, to look for clues about how “Freddy” and “Betty” sleep. A picture of night life (the sleepy kind) really began to come to life.

Even though Betty was certain that Freddy slept much hotter, we didn’t find a significant difference in temperature between the two. Over multiple nights, we found that Freddy slept only a little warmer than Betty. The temperature of the air directly surrounding Freddy was an average of 93 degrees fahrenheit. Betty’s was 91 degrees. The biggest difference was in the relative humidity in the air around their bodies.

The humidity levels that surrounded Freddy were so very different. Freddy put off A LOT more moisture, even though they both were wearing similar-weight pajamas. The relative humidity around Freddy was an average of 57%, compared to Betty at 46%, and it also fluctuated significantly throughout the night. His standard deviation was +/- 10 percentage points. Betty’s was +/- 3 percentage points from her baseline average. Here it’s hard to believe that they are sleeping in the same bed and only a couple degrees apart.

The two definitely impacted each other’s environment. When we dug in, we saw significant spikes and dips in each’s sleep environment that appear to be directly related. 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.

Betty was super fascinated by the data. The first time I shared the info, she was like “AHAA!!!!”. She had always suspected that Freddy was a sweaty sleeper (and a sheet-stealer), but here was final, compelling proof that it was true, and it had an impact on her sleep. For us, as designers and engineers, research like this has been eye opening.

The night is an incredibly active part of our day, and we have to design for it. Colleagues of mine designed and engineered a bed sheet that supports natural airflow, they developed a custom layer for our mattress that has a little bounce but doesn’t trap heat beneath the body, and they developed a pillow that has a unique weave so it stays cool while we move about. It’s part of what’s exciting about being at a sleep company like Casper, to integrate R&D like this into each product we create. Now we just need to get a full sleep set to Betty and Freddy.