Made of tough yet flexible ABS plastic propeller bumper guards. These weigh, as it turns out, almost a gram. 1.08-1.09 respectively. But as the Proto X only weighs 11.3 grams ANY extra weight will effect flight times and flight characteristics. This will tame down the Proto X, puts a little bit of "whoa" on zippy here. Very simple and have made flying my Proto X much less prone to prop damage and loss. Not a guarantee, just less likely. Must have for beginners and kids until they get the hang of it. And honestly I cruise mine around all the time with it on regardless. Mostly because I am reckless with this little gem on my Proto X. ;0) Another bonus I've found is it seems to land on its feet more often with it on. Can't explain it as you would think with the heavier top it would flip on its head, but 8/10 times if I crash I find it right side up. Attached with heavy duty double sided tape(provided). I have actually broken the ring more often than before the tape lets loose. Make sure you check your prop clearance for each prop and twist the guard accordingly. I also attach the adhesive to the canopy first and then line up the guard. Make sure to press firmly but don't press hard enough to break your quad. Rings are super glue-able. I have a coworker who used hot glue to attach his, but I find that method adds too much weight. Personal opinion. FDM, 200 micron resolution. 1.75mm ABS. Full Fill. Fine Printing.