NOVELTY - Mixed polyether comprises polyether polyol comprising a mixture of polyether polyol I including sorbitol, sucrose, pentaerythritol and glycerol, polyether polyol II including sorbitol and triisopropanolamine, polyether polyol III including sorbitol and water, and polyether polyol IV including glycerol as initiator for propylene oxide ring-opening polymerization having specific functionality, catalyst comprising mixture of pentamethyldiethylenetriamine, dimethylcyclohexylamine, dimethylbenzylamine and 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, silicone oil, water and foaming agent.    USE - The mixed polyether is useful in solar water heaters (claimed).    ADVANTAGE - The mixed polyether: has high strength in comparison with polyether prepared using rigid polyurethane foam plastic; has more fine and smooth foam; and has lower coefficient of thermal conductivity. The method is carried out at room temperature, thus saving energy, and reducing energy supply device and complex operation.    DETAILED DESCRIPTION - Mixed polyether comprises 100 pts. wt. polyether polyol, 2.1-4.3 pts. wt. catalyst, 1.5-2.5 pts. wt. silicone oil, 1.5-2.5 pts. wt. water and 15-20 pts. wt. foaming agent. The polyether polyol is a mixture of 40-50 pts. wt. polyether polyol I, 20-30 pts. wt. polyether polyol II, 15-20 pts. wt. polyether polyol III, and 10-15 pts. wt. polyether polyol IV. The polyether polyol I is sorbitol, sucrose, pentaerythritol and glycerol as an initiator for propylene oxide ring-opening polymerization with functionality of 3.8 and molecular weight of 800. The polyether polyol II is sorbitol and triisopropanolamine as an initiator for propylene oxide ring-opening polymerization with functionality of 5 and molecular weight of 680. The polyether polyol III is sorbitol and water as an initiator for propylene oxide ring-opening polymerization with functionality of 4 and molecular weight of 590. The polyether polyol IV is glycerol as an initiator for propylene oxide ring-opening polymerization with functionality of 3 and molecular weight of 370. The catalyst is a mixture of 0.1-0.5 pts. wt. pentamethyldiethylenetriamine, 0.5-1.5 pts. wt. dimethylcyclohexylamine, 1-1.5 pts. wt. dimethylbenzylamine and 0.5-0.8 pts. wt. 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine. An INDEPENDENT CLAIM is also included for preparing the mixed polyether, comprising introducing a foaming agent into a foaming agent mixing tank, continuously mixing by a circulation pump to form uniform and stable liquid, mixing with polyether glycol, silicone oil, water and catalyst, and uniformly mixing to obtain the product.