PSA (Pressure-Sensitive Adhesive)
Affiliate link — we may earn a commissionPSA sanding discs have a peel-and-stick adhesive backing, like a giant sticker. You peel the paper off, press the disc onto the sanding pad, and it stays put. PSA discs cost 20 to 30% less than hook-and-loop discs for the same grit and diameter. The downside: once you pull a PSA disc off the pad, the adhesive is mostly spent. You can't reattach it cleanly. So if you need to check the surface mid-sand and then keep going with the same disc, PSA makes that hard. Some pads accept both PSA and hook-and-loop discs. Others are built for one type only.
Why It Matters
If you're doing production work and burning through discs fast (refinishing floors, body work, heavy sanding), PSA is cheaper and you're changing discs constantly anyway. For general woodworking where you pull the disc off to inspect, switch grits, and sometimes reuse a half-worn disc, hook-and-loop is more practical.