How Shapewear Works

Squeezing the Fat
Spanx founder Sara Blakely attends the launch of Haute Contour by Spanx at Saks Fifth Avenue on March 26, 2009 in New York City. Joe Kohen/WireImage/Getty Images

Spanx's founder Sara Blakely stumbled upon her idea for this new style of shapewear when she was annoyed that she couldn't smooth out the panty line visible under her pants. She ended up cutting off the feet from a pair of control-top pantyhose and wearing that underneath [source: Wood]. Blakely sensed a business opportunity, but to get there, she had to turn to material science in the form of spandex.

Spandex fiber (also known as elastane in Europe) was invented in the 1960s for ladies' undergarments and as a replacement for rubber [source: Reisch]. The fibers, essentially complex types of polyurethane, are incorporated into a fabric, like cotton or polyester, allowing the material to maintain its shape and not stretch out, no matter how much you squeeze into it. Spandex is the perfect material for turning bodily bulges into sleek silhouettes because it can stretch up to 600 percent and then return to its original size. DuPont manufacturers spandex fiber under the brand name Lycra [source: Reisch].

Modern shapewear like Spanx uses a combination of elastic and rigid fabrics, sewn or knit together in different patterns, that result in accentuating particular shapes. The nipping and tucking that these undergarments achieve is able to give the appearance of a 5-15 pound- (2-7 kilogram-) weight loss [source: Walters].

But we all know that women aren't really losing that weight when they squeeze into a pair of Spanx, so what is going on? Where does the fat go? As many of us know from personal experience, fat is ... well ... squishy. It condenses easily and its fluidity means it can be pushed into tiny empty spaces in our bodies, like the spaces that open up when muscle is compressed. So, the fat can easily be hidden away by just smooshing it inward.

But shapewear does more than just hide fat. The placement of the seams and types of fabrics that are used can actually move fat directionally, relocating it to more desirable areas. If you like a bigger rear end, for example, there's probably some shapewear that can shift fat around to give you a bit more cushioning in your behind.

However, some reports say shapewear may cause blood clots, acid reflux, and breathing problems [source: Adams]. As the garments compress the stomach, intestines and colon, the flow of digestion may be stifled, leading to temporary discomfort. Issues can arise on the outside of the body just as much as the inside. Because the tightly fitting material can trap moisture, it can create an environment ripe for bacterial and yeast infections.