Polyvinyl butyral (PVB) is a resin prepared from polyvinyl alcohol by reaction with butyraldehyde. PVB is an important material that has a wide range of uses in applications that require strong binding, optical clarity, excellent surface adhesion, toughness and flexibility. The most well-known application of PVB is in laminated safety glass, for example, in the windscreens of vehicles. In such products, PVB is used as an interface layer between two sheets of toughened glass. The interface layer absorbs the energy of impacts, binding broken shards of glass together and distributing the force of the impact over a wide area. The use of laminated glass has greatly reduced injuries resulting from automobile accidents. As it is the viscoelastic properties of PVB that contribute to its performance in glass laminates, the molecular weight distribution of the material must be closely monitored to ensure optimum performance. Gel permeation chromatography (GPC) with triple detection, employing a light scattering detector and viscometer, may be used to determine accurate molecular weights for polymers such as PVB. Three PVB materials were analyzed using these techniques, one of which did not perform as expected in application testing.