What Makes Soft Things Soft?


Thanks to Skillshare for supporting this episode
of SciShow. Click the link in the description to learn
more about Skillshare. [ ♪ Intro ] If you’ve ever run your fingers over a comfy blanket
or buried your face in a fluffy cat after a bad day, you’re familiar with just
how nice the sensation of softness can be. And people are willing to pay for it. You’ll see bed sheets proclaiming the sumptuous
goodness of Egyptian cotton or cashmere scarves retailing for a small fortune. But why do cashmere and these other soft fabrics
feel so soft?! Well, the answer isn’t completely clear,
but it seems to involve two main components: the properties of the material you’re touching,
and you. Or rather, your brain. Fabric hand, or handle, is the term the textile
industry uses to describe the way a fabric feels and moves when you touch it. For years, scientists who study fabric hand have been trying to relate the subjective words we use to describe textures, like “soft” or “crisp”, to properties they can actually measure. And it can get pretty complex. The feel of the fabric can be influenced not
just by the material properties but also by the way you touch it and whether or not you’re actively moving your fingers over the material. And your definition of “soft” might not match mine, which makes things even more complicated. Despite this, scientists have pinpointed material
properties that could be related to softness. These can be split into two main groups: how
smooth the fabric is, which includes properties like friction and surface irregularities, and how easy it is to compress, which includes properties like the flexibility of the fabric. So a bean bag sofa is soft not only because
of its fabric casing, but also because you can squish it really easily. But soft doesn’t necessarily mean you
have the smoothest, most compressible object in the world. A 2006 study showed that even though alpaca
fiber was 10 times as rigid as wool, we encounter less friction when touching alpaca, so it
feels softer. So material properties are part of the story,
but clearly there’s more to it. And that “more” is in our brains. We don’t understand everything about how
it works yet. But two psychology studies that examined how
people rated the softness of compliant objects may provide clues as to why. Compliance, which can be measured by compressing
an object, is a way of describing how objects deform when they are subject to forces. In 1995, scientists found that your perception
of softness could be related to the way that pressure is distributed on your fingers as
you move them over an object. At least in the case of objects with deformable
surfaces, not so much for rigid ones. The researchers performed a series of experiments
that involved, among other things, people using their finger to press down on rubber,
and having rubber pressed down on their finger. The results suggested that tactile information
is enough to tell us whether something’s soft. This information is communicated by mechanoreceptors in our skin that work by sensing differences in pressure on your skin when your finger touches an object. A study in 2008 extended these findings and
found that people tended to rate rubber objects as soft if they were more compliant or deformable
than the human finger, and hard if they were less compliant. So whether you’re petting your dog or just
gliding your hand over a bunch of luxurious cashmere scarfs, there’s actually a lot
going on to bring you that lovely experience. So, cashmere scarves are a treat to touch. But cream mixing with coffee can be a treat
for your eyes. Just picture it, a nice glass of cold brew
with that perfect swirl of cream. And if you wanted to capture that moment forever, Skillshare offers a course on how to photograph coffee swirls. In the class “Cold Brew Coffee Swirl,”
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