I've been doing a bunch of cutting on the 1/8" birch from WoodCraft for a design I'm perfecting, and after trying the plastic masking film someone recommended, I decided that paper film would be better. Well lo and behold a friend just happened to have two large 12" rolls of paper transfer tape for transferring sticky-back nylon laying around his shop that I happened across. It's labeled Masking Angel Tape. It's the same cream color as standard masking tape and has a medium tack I'd guess. I tried it out today and while it masked the char well, it also left behind a nasty residue from the burnt glue at the edges which doesn't come off easily. So... strike two. Plain old blue painters tape has been working the best by a long shot, so I picked up a 3-inch roll and will be using that from now on. Stick with what works. I've seen on some 3D printer groups (they use it to print on) that they bulk order it in larger rolls ... 6 inches or more... so that might be the way to go for larger cuts in the future.
I've updated the materials database with the above mentioned birch... and have some 1/8" bamboo ply on the way from Inventables.com. Not cheap at $8.56 per square foot plus shipping, but I used the $20 gift card that came with the laser to buy it, so we'll see if it's worth the money. It can be had for cheaper in much larger sheets.