If you have friends in Germany or Austria, ask them to send you a tube of Hirschtalg, a creme. You rub a small amount all over your feet and ankles before you begin to walk. It costs about €5. I believe it comes from the fat of deer. I have used it a good bit, and it prevents chafing and blisters. Also, in Spain, you can buy Unguento Tradicional, a creme with aloe vera, camphor, arnica, eucalyptus, and other nice things. You can put it on your feet before and after you walk. Many albergues sell it in small sachets, enough for one application. I bought a 100ml container in Los Arcos and was charged €19, (I won't name the shop), and in Belorado it was for sale for €10. Be sure to have a very thin pair of socks next to your skin, and a thicker pair over them. You should do this anyway, regardless of whether you use vaseline, compeed, Hirschtalg, Unguento, nothing at all, or anything else.