In a nutshell

The Undercovers are composed of pads of thin gray adhesive double-sided foam (Stickies) and white, gray or black felt pads (10 each) which fix a lavalier capsule on the skin while gently protecting the capsule from clothing and wind rubbing.

Our recommendations

The adhesive pads are hypoallergenic and disposable. Clean the skin with a degreasing makeup product before use. Respect actor's hair when removing.
The felt pads can possibly, and very carefully, be recovered.