Looking at Super-Soft Textiles Under a Microscope

Activate lab coat.

During my R&D for the Casper sheets, we looked at a lot of cotton yarn under microscopes. What we found is that when it comes to cotton fiber, length really does matter. It’s the key to what makes something soft and long-lasting or (not).

Cotton is wild. I mean that metaphorically, but it can also be true literally. There’s Asiatic cotton, which is native to India, Upland cotton, which is native primarily to Latin and South America, Egyptian cotton, which is native to (you probably already guessed) Egypt, and Pima cotton, which has been cultivated in the Southwestern United States since the early 20th century.

The label “100% cotton” says less about a textile than it sounds. Upland cotton has a medium-length fiber. Egyptian cotton has a long fiber (and the best of it is grown on the banks of the Nile). Pima cotton has one of the longest cotton fibers in the world, and there are big farms where it’s cultivated in California. Each species of cotton has unique characteristics.

The reason cotton species are so important—to whether a textile like a t-shirt or bed sheet comes out soft or scratchy—is because of how cotton textiles are constructed. Textiles are woven from yarn, and yarn is woven from fibers. As short or even medium-length cotton fibers are wound around each other to create a yarn, they don’t lay flat on a microscopic level. They stick up like grass. The resulting feeling is scratchiness. As long fibers are wrapped around each other to create a yarn, they lay flat. The resulting textile feels soft, smooth and gets better wash after wash, not weaker. That all gets back to the species of cotton used.

Sometimes, manufacturers try to mask the natural properties of the type of cotton they’re using. During our R&D, we noticed that some t-shirts, bed sheets, and other textiles no longer feel soft after a few washes. It’s because manufacturers sometimes add chemical finishings, e.g., silicone, to textiles in order to mask underlying scratchiness and help them feel soft. The problem, however, is that these finishings wear or wash off quickly. A lot of boxed-in-the-garage tees or bed sheets may have had a lot of chemicals on them to begin with.

To get the best sense of how something will wear and feel, look at the species of cotton. American Pima is 35% longer than standard cottons, and Supima is a branded version of Pima that can be traced directly back to its source, with much of it coming from a farm in central California. It’s the one we ended up selecting for the Casper sheets, and along with authentic Egyptian cotton, is one of the best fibers in the world.

And that’s just the beginning.