A polytunnel (also known as a tunnel greenhouse, hoop greenhouse or hoophouse, or high tunnel) is a tunnel made of polyethylene, usually semi-circular, square or elongated in shape. The interior heats up because incoming solar radiation from the sun passes through the polyethylene covering, which is transparent to visible light, and is absorbed by the plants, soil, and other surfaces inside. This absorbed energy is then re-emitted as infrared radiation, which the polyethylene material traps, preventing it from escaping back into the atmosphere—a phenomenon similar to the greenhouse effect. This trapped heat creates a warmer microclimate inside the polytunnel, allowing for extended growing seasons, protection against adverse weather conditions such as frost, heavy rain, or strong winds, and the cultivation of plants that might otherwise struggle in the local climate. The structure is typically supported by a frame, often made of metal or galvanized steel hoops, which gives it its characteristic shape and stability, making it a versatile and cost-effective solution for both small-scale gardeners and commercial farmers.
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