A panel for constituting sound insulating wall is provided with a front plate, a rear plate, and a sound absorbing material put between the plates. The sound absorbing material contains reduced plastic products coated with magnetic material such as magnetic tape and magnetic sheet. The front plate is provided on the sound source side and constituted of a plate having numerous holes. The sound absorbing material is composed of a permeable bag and the reduced plastic products in the bag so that the apparent specific gravity and permeation resistance can be 0.05-0.4 and 3-90 dyn.S/cm4, respectively. The reduced plastic products may be reduced plastic products alone not subjected to other processings, or may be a mixture of reduced plastic products and molded bodies of reduced plastic products. Alternatively, only molded bodies of reduced plastic products can be put in the permeable bag. Therefore, an inexpensive panel for constituting sound isolating wall which has an excellent sound absorbing characteristic, a moisture resistance, a water resistance, and a light weight can be fabricated by utilizing plastic products coated with magnetic material such as magnetic tape and magnetic sheet, and particularly scrap of plastic products.