PURPOSE:To obtain a heat accumulating mat fit for a greenhouse to keep warmth during night, by filling hollow spaces made between two soft, lengthy sheets when they are joined together with heat accumulating agent which changes its form from solid to liquid and vice versa at a specified temperature. CONSTITUTION:Two strips of lengthy sheet 1 and 2 made of soft material such as vinyl, rubber, etc. are joined together into a form of a sack with adhesive agent or by fusion welding on their both end edges 1a and 2a, and both seluedge edges 1b and 2b, respectively. They are also joined together in the longitudinal direction at proper intervals to form a cell 4 between each joint 3 and the next one. Each cell 4 is filled with heat accumulating agent which changes its form from solid to liquid and vice versa at a temperature from 20 deg.C to 30 deg.C.
