I use thin, cheap muslin for my foundations. I have also used lightweight interfacing ( about the weight of a dryer sheet) the sew in kind of lightweight interfacing I can usually get at Joanne’s for about 99 cents ayard. Then you don’t have to remove it. It doesn’t add any noticeable weight. String quilts tend to be heavier than regular pieced quilts anyway. Sure beats the aggravation of paper removal