studio window question
I'm building a studio from the ground up and I'm currently working on installing my interior windows. I've read in several different places that I need to apply a rubbery mastic sealer between my window frame and wall casing. I've been to several DIY stores and no one seems to know what I mean by rubbery mastic. Does anyone know of a brand name for this kind of material? I've also considered using 100% silicone. Anyone have any suggestions? Thanks!
Phillip