<UL><LI>Black sandpaper is made from aluminum oxide</LI><LI> Great nail coverage</LI><LI> Large surface area</LI></UL><BR/> Beauty Secrets Black Rectangular Cushion Nail Files features a 100/100 grit and 100/180 grit that is great to file acrylic nail extensions to a thinner consistency. A large surface area allows for a longer file life.