I'm sorry to write a bad review. I purchased 3 pair or leak proof undies. I purchased my regular size M. The website claims "invisible under anything". I was excited to try them on. They were so tight, they made VISIBLE PANTY LINES. I did not like this. I emailed customer service asking for a refund. Later to find out Knix does not offer refunds on unworn undies. Since I had only worn one pair, I thought I'd be able to return the other two. In the first response Customer Service said to wear the underwear, wash them and they will stretch out. They did not address my question. After writing back for another refund I mentioned the last three companies I've purchased undies from (Victoria's Secret, Madewell and Thirdlove) all have at least a 30 day refund on unworn product. I think Customer service is subpar, although quick to respond. I also think Knix would be wise to review their return policy. Sorry for such poor policy.