I use self-adhesive weather stripping. You can find it at Home Depot. It's a roll of foam that's roughly an inch around on each side and has a self-adhesive back. Just cut small lengths of it and place it where you need it.
Works great for gauntlets 
To anyone else interested, it can also be used to pad a helmet, or to make Stormtrooper armor fit more closely (in the arm pieces. It also can be used to reduce pieces rubbing against each other, chipping paint or gloss-finishes, and helps cut down on that clacking noise from the pieces hitting each other.
Great stuff,
Phil