PURPOSE: To improve development of erack on a molded products, due to repeated dipping in water or hot water, by molding a copolymer of methyl methacrylate with styrene, having a specified composition ratio and MW.

CONSTITUTION: A styrene-methyl methacrylate copolymer of number-average MW50,000W300,000, total light transmittance ≥85% and haze ≤2%, composed of 70W15pts.wt. of methyl methyacrylate and 30W85pts.wt. of styrene, is molded. A weight ratio of methyl methacrylate to styrene >70/30W15/85, is not effective for improving development of crack due to repeated dipping in water or hot water, and that <70/30W15W85, can not give transmittance or haze sfficient for excellent transparency, required for the molded product. A copolymer of number-average MW larger than said range, is of inferior fluidity when molded and one with the small MW than said range, gives a molded product of exceeding by reduced strength.