A method for stabilizing material physical properties of recyclable bumpers including the steps of: separating coating from raw material obtained by cleaning, fracturing and drying recyclable bumpers to form a recycled matrix; mixing an additive with the recycled matrix; melting and extruding the mixed matrix with an extrusion machine; cutting the molten and extruded matrix to produce pellets; introducing the pellets into a tank of a predetermined capacity; and mixing the pellets in the tank for a predetermined period of time while again delivering the pellets in the tank to an introduction opening of the tank for reintroduction into the tank in parallel with the pellets that are to be newly introduced.