The mold is only partially filled, and injected plastic expands to fill the mold to produce a part that is light weight because of the entrapped porosity, but the skin is integral.

• 通常部分填充模具，并使注入的塑料膨胀来填充模具，制成具有很轻重量的制品，这些轻制品是由于引发产生了孔状结构，但是制品的表皮是实心的.