Standard greenhouse glass or 3mm horticultural glass as it’s known is the cheapest greenhouse glazing and is in 2 pieces per panel. The individual panes measure 2ft x 2ft, overlap mid way on each section of the greenhouse and are then held together with "S" clips.
Toughened Safety Glass
Toughened safety glass in 3mm and 4mm thickness, if impacted hard will only shatter into hundreds of tiny pieces like a car windscreen that are relatively harmless, whereas standard greenhouse glass will break into long shards. Toughened glass is also supplied in long panes which run from floor to eaves giving a smooth easily cleaned surface. Toughened glass is also heavier than standard horticultural glass and polycarbonate which gives excellent wind resistance, the wind won’t be shifting it, that’s for sure!
Toughened glass is made by passing normal cut glass through a high temperature furnace that heats up the outside of the glass very quickly, creating tension on it’s surface that hardens the glass. This glass will take an impact from the kid’s football without a problem, but not a golf or cricket ball.