The SierraBlaster does not work as well on soft materials or materials with many cracks or foliations. The gasses escape out the cracks before the propellant can initiate the synergistic loop required to create significant pressure. This does not mean the SierraBlaster can not work on soft or cracked materials. It means the learning curve is higher and the maximum effectiveness will be diminished. See the Technical Overview for more information on the synergistic loop.