It is a small, fingerless, gray leather glove, with straps on it to adjust for the wearer. It fit the hands of a fully grown human, but had also been used by children.
The glove can turn the wearer invisible if they are motionless. The person may breathe, blink, and talk without detection, but anymore movement will render the wearer visible. The glove is unable to mask smell, which means that some predators or enemies may not be fooled.
Rise of the Evening Star
When Coulter and Seth ventured into the grove in the valley of the Four Hills, they were both overwhelmed by fear. Coulter managed to save Seth by giving him his magical cocoon, in the process also handing him his invisibility glove.
Seth later used it to infiltrate the Fablehaven house, stealing the key to the inverted tower from Vanessa Santoro and Christopher Vogel. After Seth defeated the Revenant, Kendra received the glove to help her during the raid on the Inverted Tower, where she used it a few times.