There are three options for glazing in most greenhouses -
- Horticultural Glass, Toughened Glass or Polycarbonate. A few greenhouses also use Perspex.
- Horticultural glass comes in 2'x2' squares, is quite brittle and when it breaks it shards into sharp and dangerous pieces.
- Toughened glass comes in large panes, is much stronger than horticultural glass, adding strength to a greenhouse. If it breaks it shatters like a car windscreen, leaving small granules of glass.
Polycarbonate comes in large sheets. It is lightweight and flexible, but has a number of limiting factors: it can easily pop out when the wind gets up, it is opaque so you cannot see through it, it is a sandwich with cavities in it that fill with water and algae over time. And if that does not put you off polycarbonate it is also the most expensive option!
Perspex is used where the design of the greenhouse requires a curved glazing shape.