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Leggings are a great addition to any wardrobe. They let you stay comfortable wearing short skirts and tunics in cold weather, work well for layered looks, and make comfortable fitness wear. Not all leggings perform the same, however. Nylon, a manmade fiber, insulates less than cotton, with a higher gloss and translucency, while cotton is softer, less slippery and more resistant to heat. Which material is best for your leggings depends on how you intend to wear them.
Nylon was originally produced as a manmade alternative to silk. This material is made from petroleum derivatives and has a smooth, slippery surface that makes nylon leggings look a little shiny. Nylon leggings also are more likely to be just a little see-through, making some versions a bad choice for wearing alone. Cotton leggings are a lot more opaque and have a dull surface that won't reflect light. They can be worn on their own or under your other clothes.
Nylon doesn't have the same ability to keep you warm in cold weather that cotton does. It also breathes poorly and is more likely to trap moisture against your skin, since manmade nylon fibers can't wick it away. That means that nylon leggings may be less comfortable in extreme temperatures or for people with sensitive skin. Nylon's base doesn't provide food for fungus or mildew. Cotton can harbor microorganisms if you store it damp.
Nylon fibers tend to be stronger than cotton and resist abrasion better, so leggings made from them may be less likely to tear. This material can be weakened by exposure to sunlight, however. If you store your nylon leggings where the sun can get to them, you may find them faded or brittle in some spots. Cotton is a relatively strong material for making leggings, but not as strong as nylon. It can be weakened by bleaching or if it rubs against other fabric, a bike seat or any other object for a long time. Cotton leggings also can tend to pill over time.
Cotton resists heat better, standing up to hot irons and dryers without any problems. Nylon, on the other hand, will melt if you expose it to too much heat and can be a fire hazard if worn near an open flame. If you're looking for a pair of leggings to wear camping or close to a fireplace, you may want to stick with cotton.
Most leggings aren't made of pure cotton or nylon. Instead, they contain at least a little material for stretching. This stretchy material is made up of many tiny threads of polyurethane rubber and helps the leggings fit closely. It also slightly changes the properties of the fabric, making cotton a little less breathable and a little less heat resistant. Nylon leggings may be slightly less durable with the addition of elastane, since they lose their ability to fit well if the elastic fibers break or fray.