It's mainly keratin Jem, which is one of the main components of hair. They put it through your hair then dry and straighten on a high heat which seals the keratin into the hair. You then have to leave it for 4 days without washing, but after that it's fab - you can leave your hair to dry and you don't need to use the straighteners which means your hair gets a rest. It leaves it really well conditioned and it just gradually washes out after a few months - not like a perm where it grows out and you have half straight and half curly hair. They can cost anything from £90 to £250, but I got a groupon voucher for £50 (even then it was a big treat for myself!).