"DOUBLE-ROLLED knitting" - the same general idea as thrumming, but with not so much fiddley prep. Add a thick layer of roving inside your knitting, for warmth and padding. "With each knit stitch, wool pencil roving is brought under and then flipped over the knitting yarn, creating a full loop of roving around the yarn. After the flip, complete the knit stitch as usual. Only the yarn is used to knit the stitch, not the yarn and roving together."