I’m working with a client on her “MadMen” dress, and I advised her to preshrink the zipper for the dress. She had already preshrunk the wool fabric. Here’s her technique — a mug of hot water! Anyway you do it, the principle is to shrink that item as much as it is going to shrink, so that it stays the way you sewed it in after you wash it. Now, Claire might dry clean her dress instead of wash it. The fabric she chose is a medium-weight wool — beautiful fabric that zips along nicely under the needle — but the preshrunk notions give her either option. Thanks for the pic, Claire!