Solid vinyl. All roll-up signs meet MUTCD requirements. Fiberglass ribs, or cross bracing, feature a protective veil to prevent blooming and painful splinters. The rib set is fastened at the center with a 1/4" steel rivet and spring washer providing constant tension. It will not loosen or tighten with use the way nut and bolt assemblies do. Rectangular and delta style corner pockets are made of tough polycarbonate plastic for durability. Delta pockets on the horizontal corners provide three rivet points for durability and a shallower pocket depth for easier deployment. Delta pockets have a narrow width and feature a channel for the strap which provide a smaller, tighter diameter for easier storage. Back to back hook and loop strap for storage.