Composite laminate interlayers for a glass laminate comprising a sheet of polyethylene terephthalate (PET) layer (203) between layers of plasticized polyvinyl butyral (PVB) adhesive layers (202, 204), wherein at least one of the PVB adhesive layers is stiffened, e.g. by reduction in the amount of plasticizer, and has a glass transition temperature greater than 35 °C. The PET is preferably 0.075 to 0.25 mm (3-10 mils) thick and can have a functional coating (407) for reducing radiation, e.g. UV or IR or visible light, transmission through the glass laminate. The laminate can also comprise at least one elastomeric layer (406) adapted to reducing sound transmission through the glass laminate. The laminates exhibit enhanced maximum flexural modulus of greater than about 350 Newtons/centimeter.