Greenhouse plastic is the cheapest way to create a greenhouse. It is light, so it can be attached to almost any frame, even the side of a wall and the ground. Most often it is used for temporary greenhouses that are constructed in early spring to get a head start on the growing season.
The most common type of greenhouse plastic is 4mm polyethylene film which can be easily cut to any shape and layered for more insulation properties. 6mm is also a popular thickness. It lasts for about 3 years, much less then glass but it is about 1% of the cost of glass. It can yellow with age, and sags in the plastic can cause further problems as well as looking bad and cheap.
Greenhouse plastic is secured with special polyethylene patching tape and secured to the frame with batten tape. Bubble wrap is also used as an insulating layer in plastic greenhouses and is secured in similar ways but blocks more light than without it. Plastic is delicate, animals can puncture the film and steal food at night and kids can accidentally put an arm or leg through during the course of their activities.
