e composed, for example, of polyesters such as PET or PEN [poly(ethylene naphthalate)], polypropylene, or polyethylene such as HDPE. The middle layers, often called ???barrier??? or ???adhesive??? or ???tie??? layers, are composed of one or more combinations of either PET, PEN, carboxylated polyethylene ionomer such as Surlyn???, vinyl alcohol homopolymers or copolymers such as poly(vinyl alcohol)