A polyswitch is a conductive skin on a heat-sensitive membrane that, when heated from excessive current, expands and separates the conduction regions, drastically reducing conduction (increasing resistance). This reduces the passthrough current significantly, protecting any downstream devices of limited power capacity. Once the applied voltage has been reduced, the device contracts sufficiently to bring the conductive regions back in contact. The thermal time constant of this action is lower (quicker to respond and reset) with the smaller polyswitches (physically smaller/lower current), which is appropriate for fragile devices like tweeters.