Abstract High density polyethylene (HDPE) geomembranes have been used extensively during the last decade and very low density (VLDPE) geomembranes have been introduced during the last few years. Both materials have properties that are desirable for particular applications. HDPE has excellent chemical resistance, UV resistance and high modulus. VLDPE is very flexible and is capable of much more elongation in field applications than HDPE. A geomembrane made by the coextrusion of HDPE and VLDPE has several advantages over geomembranes made from either HDPE or VLDPE alone for many applications. These advantages are realized due to synergistic effects that occur between the two polymers, resulting in a product that incorporates desirable properties of the two materials and eliminates some of the less desirable ones. The Coextruded Multilayer Sheet (CEMS) addressed in this paper has better tensile strength, tear resistance, seam strength, chemical resistance, permeability and UV resistance than VLDPE and better puncture resistance, elongation and stress crack resistance than HDPE. Coextruded, multilayer geomembranes make available more options for the design engineer attempting to find the best product for a given application.