<P> A greenhouse (also called a' glasshouse', or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown . These structures range in size from small sheds to industrial - sized buildings . A miniature greenhouse is known as a cold frame . The interior of a greenhouse exposed to sunlight becomes significantly warmer than the external ambient temperature, protecting its contents in cold weather . </P> <P> Many commercial glass greenhouses or hothouses are high tech production facilities for vegetables or flowers . The glass greenhouses are filled with equipment including screening installations, heating, cooling, lighting, and may be controlled by a computer to optimize conditions for plant growth . Different techniques are then used to evaluate optimality - degrees and comfort ratio of greenhouse micro-climate (i.e., air temperature, relative humidity and vapor pressure deficit) in order to reduce production risk prior to cultivation of a specific crop . </P>

What is the green house made out of