Although this was somewhat large for an extra small it fits a medium person I really love it. It is a stretchy form of silk that is almost hard to believe is really silk. I'm not sure how you test for that? I did a little burn on some of the thread to see if it smelled like hair which is a test I saw online and it didn't really have a smell. It is warm and comfortable and I would like to think it is real silk but I wish I had a better way to confirm that. It definitely feels silky but almost more like a polyester blend. It is very comfortable so please don't let this make you not buy it. I wear it everyday almost under my clothes for warmth and comfort. I wish I could find third-party confirmation online that it is definitely silk but other than some reviewers or say they think so and others who say they think not I don't know?