Innovative zirconia grit gives Dewalt Type 29 flap discs the power to remove material 3 times fast than fiber resin metal sanding discs. Type 29 fiberglass backing provides a grinding angle of 20-25 degree. A premium abrasive cloth offers a life up to 15 times long than fiber resin metal sanding discs. Zirconia cloth provides faster grinding action than standard flap discsPremium abrasive cloth provides up to 15 X longer life than fiber resin metal sanding discsType 29 fiberglass backing provides grinding angle of 20-25 degrees