Elastic

in Materials Science the word elastomer refers to a material which is very elastic, like rubber. The word elastic is often used colloquially to refer to an elastomeric material such as rubber or cloth/rubber combinations.

holding things together, e.g. with a rubber band

flexibly moving something over a thick to a thin part, as in clothing put on over the head, hips, hands, feet, and elastic necklaces, bracelets, watcharmbands. An alternative in many of these cases (not for socks) is a closing device such as buttons, a zipper, laces, Velcro, a buckle, a snap

flexibly making airtight or fluidtight connections as in a hose or condom

flexibly cushioning (a shock absorber) as with tires and for the soles of shoes, and under the legs of chairs, under vibrating equipment, on a door or door-post, on bumper cars, etc.

Elastomers: Materials That Stretch and Return

Elasticity is a behavior before it is a product: a material is stretched, and when the force is released it returns to its earlier shape instead of staying deformed. In materials science the word elastomer refers to a material which is very elastic, like rubber. The word elastic is often used colloquially to refer to an elastomeric material such as rubber, or cloth and rubber combinations, and that colloquial use is the one clothing people meet daily, the woven or knitted tape with rubber or elastane threads inside it that is sold by the yard as simply elastic. The two uses should be kept in proportion: elastomer names the class of stretchy materials, while a garment's elastic names a component, the strip, cord or thread of such material built into the clothing to do a specific job.

In clothing the job is almost always the same problem stated in different places: the body is not a uniform cylinder, and garments must pass over its wide parts and then grip its narrow parts. Elastic solves it by flexibly moving something over a thick to a thin part, as in clothing put on over the head, hips, hands and feet: a waistband stretches over the hips and settles at the waist, a sock's elastic top stretches over the heel and grips the ankle and calf, a cuff stretches over the hand and closes at the wrist, and a neck opening stretches over the head and recovers at the neck. Elastic also holds things together more generally, as with a rubber band, and appears in elastic necklaces, bracelets and watch armbands that size themselves to the wearer without a clasp setting. A garment with elastic in the right places needs no exact sizing at that point, which is why elastic is the fitting system of underwear, swimwear, hosiery and much casual clothing.

Elastic Versus Closures, and Stretch Beyond Clothing

Elastic is one answer to fastening, not the only one. An alternative in many of these cases, not for socks, is a closing device such as buttons, a zipper, laces, Velcro, a buckle or a snap. The comparison clarifies when each is chosen. A closure opens fully, so a garment need not stretch over anything, and it can be adjusted to set points; elastic gives continuously, adjusts itself, and never comes undone, but it cannot be loosened at will, it presses constantly where it grips, and it fatigues with heat, age and washing until a waistband that once recovered hangs slack. Socks are the telling exception in the comparison: no one would button a sock, because the grip must be continuous around the leg and the garment must be pulled on in one motion, so elastic is not merely convenient there but the only workable system. Good garment design often combines both, a zipper or button opening where entry is needed and elastic where continuous gentle grip is needed.

The same stretch-and-return property does work far beyond the wardrobe. Elastomeric materials flexibly make airtight or fluidtight connections, as in a hose, where a stretched sleeve seals over a fitting, and they flexibly cushion as shock absorbers, as with tires and for the soles of shoes, and under the legs of chairs, under vibrating equipment, on a door or door-post, and on bumper cars. In each case the principle a waistband uses is at work at another scale: deform under load, absorb or seal, and return. Back in sewing, elastic belongs with the trims and notions a dressmaker or tailor chooses among, alongside bias tape, which stretches by its cut rather than its fiber, zippers, Velcro and other trimmings. Knowing which kind of stretch a job needs, the cut of the cloth or the recovery of an elastomer, is a basic judgment of garment construction.