Sew foam questions for all the trimmers I tend to glue most pieces (specifically on seats) as it seems to make the whole process a little easier with the same quality end product. This is especially true when sewing pleats or diamonds or whatever in my eyes. However, on backrest covers, I just spray the top of foam and not backside of material, that way it doesn't really "stick" but it makes it easier to sew yet doesn't wrinkle as easily when rolled onto the seat. Also when putting on the seat covers, even on cushions, I steam the backside of the foam really well just before installing. It releases the glue for a minutes so you don't get stubborn wrinkles. Every project is different though.