A neck sweat "sweats" off excess leather. It will not work miracles, but it can make a substantial difference on one with just a tick more neck than preffered. To work, it has to go on every day for most of the day. We have our best results when they also wear at the show right up until the last minute. I don't really know the science behind it. It just makes the area get hotter and then shrink up like wearing a ring for a long peroid of time.