Is there any functional difference between garnet paper and 3M wetordry sandpaper, other than the backing? I just got back into balsa kits since a kid and I'm about to make some sanding blocks using spray adhesive.
I don’t know, never heard of garnet paper. After a quick internet search, it appears to be the same or similar. I’m guessing it comes down to how particular you are. For us mere mortals, there is no difference.
Garnet paper is essentially sifted sand graded to particle size and glued onto a regular thick paper backing. Cheap and aggressive back in the day, not so much anymore. Wet or dry is essentially the same, sometimes made from silicon carbide and waterproof glue and specialty paper. Garnet is essentially no finer than 120 grit so is used for massive removal on soft woods.