Light fabric that stretches and moves well. These are great for working out, running errands, or even just laying around the house. I am usually right in between medium and large when it comes to pants. I initially bought the medium, which fit well (maybe a little tighter than the pictures online but not much). The only problem was that the fabric is thin enough that they left very little to the imagination. As much as my wife liked them, I wasn't so sure the general public would agree, so I exchanged them for the large, and they are perfect. I also need to brag on the customer service. I bought these on sale, so the website wouldn't let me exchange/return them. A quick call to their customer service number, and they had my exchange in place and ready to go within just a few minutes; I didn't even have to sit on hold or go through a phone tree. Outstanding service that will make BP the place I go to first.