ShirTailor is a brand name interfacing made by Pellon. It’s a fusible, non-woven interfacing made specifically for shirt collars, cuffs and button plackets. Despite the fact that it’s a non-woven, the manufacturers claim it has a lengthwise grain and a modicum of cross-grain stretch, so you want to pay attention to that when you’re cutting. I tend to cut non-woven interfacings a bit willy-nilly, so don’t be like me. Also, because it’s a fusible, you want to stick to cottons and other fabrics that can take the hot, damp iron required to get it to stick to your fabric.
I must admit, I haven’t used this myself, but one of my sewing teachers swears by it over regular interfacing when she’s making a blouse.