In the textile industry, recently, it is urgent to develop the recycling system of the polyester fiber waste which results from the manufacturing process of sythetic fabric. However, most of the fiber wastes are destroyed by fire or buried underground. In this paper, the insulating composites which consist of polyester fiber wastes and PLA films are molded by compression molding method. In the process of preforming, the polyester fiber wastes are arrayed in uni-direction, and PLA films are inserted among layers of the polyester fiber wastes as binder. Namely, the polyester fiber wastes layers and PLA films are laminated alternately. In this paper, pitch (distance among the fiber wastes) and number of layers of polyester fiber wastes are varied, and the effect of pitch and number of layers of polyester fiber wastes on mechanical property and thermal insulating propertiy of the composites are discussed. As the result, it is concluded here that the melted state and the thickness of layers of PLA affect largely on the thermal conductivity and the bending strength of the boards.