What polymer is the common interlayer in modern laminated auto windshields?

Polyvinyl butyral is the common polymer interlayer in modern laminated auto windshields.

Usually abbreviated PVB, this tough, flexible resin is sandwiched between sheets of glass and bonded using heat and pressure. When the glass breaks, the interlayer helps hold fragments together instead of allowing sharp pieces to scatter freely through the passenger compartment.

PVB was invented in 1927 by Canadian chemists Howard W. Matheson and Frederick W. Skirrow. By the late 1930s, laminated safety glass containing PVB had largely replaced earlier windshield laminates because it stayed clear and resisted penetration better during crashes.

PVB is the canonical quiz answer, although it is not the only modern interlayer. Thermoplastic polyurethane, ethylene-vinyl acetate and ionoplast materials are also used in some laminated glazing. Tempered side and rear windows are a different safety-glass design: they usually shatter into small granules rather than remaining attached to a flexible film.