• Flexible plastic films including polyethylene , polyester and polyvinyl chloride are used as covering material in this type of greenhouses.  Plastics as covering material for greenhouses have become popular, as they are cheap and the cost of heating is less when compared to glass greenhouses. The main disadvantage with plastic films is its short life.  For example, the best quality ultraviolet (UV) stabilized film can last for four years only.  Quonset design as well as gutter-connected design is suitable for using this covering material.