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"How does the material used in VT Feet 5 and 7 differ from normal sponge type rubber?"

  The material used in VT Feet 5 and 7 is specially designed to exhibit superior shock absorption and 
  anti-vibration qualities. It is made by an expansion process using gas developing agents and produces
  a porous rubber like product with all-round closed cells. It does not require the addition of an outer skin.

 

  Sponge rubber products are characterised by partly opened (skin/skin) or completely opened cells. 
  They exhibit inferior compression-set resistance, durability and exhibit poor vibration damping performance.