FYI, I buy the large size. I am a 5'8" woman and I weigh 10 stone. I read about the trouser blow outs and made sure I had plenty of room. I wore the butt out doing a sitting glissade
and patched it with disposable OR gown material and mefix which is a medical tape. It was good enough for a few more trips. People had told me it was the end of my pants but they were still good for trips where it wasn't raining, only windy.