Flat silk weft is a thinning form of human hair wefts. To avoid hair shedding problem, manufacturers add double-stitched to make it firmer. In other words, this hair is a weft sealed by a super-thin piece of silk base. Often, these flat silk weft hair extensions are thin flat, about 1mm in thickness and 10mm in width. The hair extensions are utterly safe to attach to your head as they have no silicone and made of pure human hair.