Acrylic Glass, also known as Plexiglass or Perspex is particularly suitable for picture frames.It is strong, yet lightweight, age-resistant and weather-proof.
Please note that this is not cheap Polystyrene! Order this to replace low quality or broken glass in existing photo or picture frames. Unlike standard float glass used in picture frames which has a greenish tinge, acrylic is totally clear. It is much safer than glass and has a much higher impact strength than glass. When smashed standard glass will break into very dangerous shards whereas acrylic tends to break into larger pieces with generally much duller and safer edges.