Unknown Fiber Contents:
Fabric Samples Above and Below
I've gotten some fabric donations, and like all the rest it went through a wash and dry cycle. It helps me to know fiber content before using the fabric, and paying attention to it during this process gives me clues.
Shake out a piece of polyester or nylon blend fabric from your washer, and it smooths fairly quickly. Cotton tends to stay bunched together, and usually has more wrinkles.
Pulling it out of the dryer is an even bigger clue because man made fibers tend to have fewer wrinkles. Notice I said tend because that's not always the whole story. Some cottons are treated with chemicals that make them wrinkle far less now. It's just hard to tell so sometimes I do a burn test to know for sure.