Acrylics are weaker than polycarbonates, but cost less. Although polycarbonates offer high impact resistance, some yellow with age. Glass is usually found on the more expensive skylights. Glass is much harder and durable than plastics and does not discolor. This is a generic term for both tempered and laminated glass.
Tempered glass is the most impact resistant.
Laminated glass is fabricated with a thin layer of plastic embedded near the center of the glass. Both types keep the glass from breaking into large, sharp pieces. Skylights are often made with a tempered glass on the exterior side and a laminated pane on the interior side. This arrangement gives maximum impact resistance while protecting occupants from falling shards of glass. Because skylights are located on the roof of a building, they can result in large amounts of unwanted summer time solar heat gains and winter time heat losses.