"Windsavers"

You need something that can be cut to the right size and glued to a reedplate. It needs to be pliable enough to bend away from the reed plate to let the reed vibrate without hitting the valve, and also to completely seal off the reed slot when the other reed is playing. It also needs to be stiff enough that it does not just fall in whatever direction gravity might pull it.

One material that is used for self-made windsavers is a synthetic fiber called Ultrasuede. Its use was pioneered by PT Gazell, whose specialty is playing half-valved diatonics. Surgical tape has also ben used, and teflon bakeware liners. Some of this is described in my recent harmonicasessions.com articles on windsavers.