Having an open chimney is like leaving a window open all the time. We don't always notice the warm air escaping, but that air has to be replaced so it pulls in cold air from around doors and windows, in fact any leaky part of the building, causing the draughts that we do notice. If you block the chimney then you keep the warm air in the home and stop the cold draughts from getting in. The Chimney Sheep is a thick wad of felted Herdwick wool on a handle. It lodges in the chimney, preventing the warm air from your home escaping while the fire isn't lit. If you want to light the fire, it's easy to take out. Then pop it back in again when the fire has gone out. It is breathable and durable and will save energy, save money, and keep your home more comfortable for many years to come.