I purchased the Mepitel film at the Mayo Clinic store in Rochester , MN where I was receiving my care. My nurse told me to buy 2 of the 15×20cm and 2 of 10× 25cm. I ended up buying one more of each part way through treatment but didn't end up using them. The nurse told me if they are unopened and you have your receipt you can return them to the store, which I was able to. Hope this helps.