Covering materials for a greenhouse vary greatly and are determined by aesthetics, maintenance, cost and light infiltration factors.
Glass is the most expensive covering material, but will transmit the most amount of light. Maintenance may become an issue, however.
Greenhouse fiberglass is specially designed for plant growth. It bends over curved surfaces, but needs to be replaced every five to ten years, depending on the quality.
Cost-efficient polycarbonate greenhouse coverings are available in many sizes. This material resists hail damage and allows good light transmission. It also has a small air channel that provides some insulation.
Polyethylene film is the least expensive greenhouse covering and may be installed in a single or double layer. If you use a double layer, you’ll need to blow air between the two layers. Poly film provides good insulation, but is the poorest light transmission of all greenhouse coverings. It needs to be replaced every few years.