A semi-flex sanding disc is a type of abrasive disc that is typically used for sanding or finishing wood, metal, and other materials. The term "semi-flex" refers to the flexibility of the disc, which is designed to be more flexible than a traditional rigid disc. This added flexibility allows the disc to conform to the contours of the surface being sanded, which can result in a more even and consistent finish.
Semi-flex sanding discs are typically made of a flexible fabric or paper material that is coated with abrasive particles, such as aluminum oxide or silicon carbide. They are designed to be used with a special backing pad that is also flexible, which allows the disc to bend and flex as it is being used. These discs are typically used for sanding curves, contours and irregular surfaces
The grit size of the abrasive particles on the disc, it can vary.