Carpet adhesives may also out-gas. Consider doing a simple test to see how out-gassing may effect you. Ask for a small piece cut directly off the roll you want to buy. Seal it in a jar and set it in a sunny window sill for a day or two. Open the jar and fan the opening with your hand.
Nylon is most popular.
It's easy to clean, very strong, resists mildew, but may be pricy. Pile describes the weave a carpet has. Loop, twist, shag, and plush all refer to the way the carpet fibers are woven into the backing. A carpet's quality is usually tied to pile thickness. Bend the carpet and see how much backing is exposed.