Structure

The coating, e.g. the number of abrasive grains per surface unit, determine the abrasive capasity.

• Open coat
  Appr. 40% of the surface is covered with abrasive grains.
  
• Semi open coat
  Appr. 65% of the surface is covered with abrasive grains.
  
• Close coat
  90-100% of the surface is covered with abrasive grains.
  

Close coat allows for deeper cutting at the start, but often increases the risk for clogging when sanding soft and resinous types of wood, synthetic materials and surface-treated materials. Therefore, an abrasive product with a more open coating may last longer even though it has a smaller number of grains per surface area.