PURPOSE:To improve the water packing property of the duct by a method wherein a specified film with continuous patterns communicating with one after another for packing water therewithin is interposed between a part of two laminated films composing of the het accumulating hot water duct for accumulating solar heat in water used in commercial gardening or the like. CONSTITUTION:As the first step for manufacturing the duct, a long and broad film 1 made of thermo-plastic resin is prepared as primary substrate. A black printing ink film 10, which serves as the film with continuous patterns communicating with one after another comprising water packing part patterns A and communicating water passage patterns B to communicate one water packing part pattern A with another adjacent water packing part pattern A, is printed on the film 1 with a gravure cylinder 2 in order to get a printed film 3. As the second step, the printed film 3 is laminated with a molten film 5 made of thermo-plastic resin with excellent light transmitting property and extruded from an extruding machine 4 as secondary substrate in order to get a long and broad laminated film 6. Because said film 10 is so capable to adhere tightly to the primary substrate 1 and to separate easily from the secondary substrate 5, the storage part for water or the like is formed between the substrates 1 and 5.
