The problem for us humans is that getting too warm is frankly more difficult to deal with than getting too cold. If it’s too cold, put something on. If it’s too warm, take something off. We can only ‘take something off’ to the point before someone calls the authorities, so we have to resort to cooling ourselves with appliances. Here’s the thing: even though cooling appliances like central air conditioning, electric fans, wall units, sticking your head in the freezer (don’t judge me) keep us, well, cool, they do require electricity to work. Let’s also not forget that these release a lot of waste heat that can actually warm up an area. A team of researchers, mainly associated with Stanford University, suggest that we could use some better textiles.
Why would we want to make better textiles to cool us off? The human body is actually a good emitter of infrared (IR) radiation, some of which is actually heat. This explains how infrared cameras work, it literally is “heat vision.”
While cotton is nice, breathable, and comfortable (speaking as a T-shirt kind of guy), it actually traps this infrared energy and warms you up. What alternatives could there be? The authors mention polyethylene, which is readily available and does quite a good job with letting IR radiation through. Now for the bad news: it doesn’t circulate air and it’s also transparent to light in the visual spectrum. In other words, it doesn’t breathe (eww) and it’s completely see-through (use your preferred commentary here). What did you expect from material associated with plastic water bottles? It should be noted that polyethylene clothing does exist: it’s Tyvek, which is personal protective gear that would be more associated with a radioactive cleanup than, say, a Starbucks. Well, unless someone spilled their pumpkin spice and plutonium latte, but that’s neither here nor there. We need something that can breathe, lets IR radiation through, but not see-through (like we would want with our everyday clothing, you know?). To that end, the authors suggest ‘nano-PE’, which is still made of polyethylene, but contains pores 50-1000 nanometers wide, much less than the thickness of a human hair. This means that light will essentially scatter within the pores instead of going straight through. Nano-PE should be able to do all three things, but can it?
Half of the paper describes how they analyzed how nano-PE performed against cotton and PE and whether it could do all the stuff I mentioned in the previous paragraph. Nano-PE can indeed let normal human IR radiation pass (they used some kind of heating element that simulated human body heat) since it only raised human body temperature by less than one degree Celsius. They would consider that better cooling than cotton (raises skin temperature by 3.5 degrees) or Tyvek (just under 3 degrees), so that’s one check. Further testing shows that while letting IR radiation through, it doesn’t let visible light through, so you may feel free to wear it without feeling self-conscious about what you’re revealing. You can also feel free to be self-conscious about other things, but that’s totally on you.
The next issue, can it breathe? Turns out that nano-PE isn’t very good with letting air circulate, even with all the pores. It’s also not very good at wicking moisture (read: sweat) from your skin, so you’re cool and probably slimy. The authors suggest a special coating and cotton mesh to help with moisture and breathing. Now it’s on par with cotton for breathability, tension (which means it could take on quite a bit of stretching before it blows out) and moisture wicking, while still doing all the good things that nano-PE can do for clothing, such as letting IR radiation through while not being transparent. It should also be noted that nano-PE is white, so the authors suggest it can be dyed. We at sci.cas suggest that it can be cooler using some YinMn Blue. You’re welcome for the idea – it’s part of the free services we provide here at sci.casual.
Nano-PE has a similar price point per square meter as cotton, but they didn’t mention how much it’s going to cost with the coating and cotton mesh. Kind of a shame, because I was thinking: YinMn Blue, self-healing, nano-PE-mesh sci.cas t-shirts (how’s that for merchandising?) All for the low, low price of probably US$300.
I clearly don’t know about branding and merchandising.
Featured Article: Hsu PC, Song AY, Catrysse PB, Liu C, Peng Y, Xie J, Fan S, Cui Y. (2016) Radiative body cooling by nanoporous polyethylene textile. Science 353(6503): 1019-1023 doi: 10.1126/science.aaf5471
Featured Image credit: Flickr/Wikimedia Commons, CC-BY-SA-20 Generic (author: Jean-Pierre)