Do not store your down sleeping bag in a stuff sack if you can help it. If it has been stored in a stuff sack for transport, take it out, stretch it out, and air it for a few days. Then, either hang the bag to store it or keep it in a storage sack. Unlike stuff sacks, storage sacks prevent the down from being overly compressed. All Marmot sleeping bags come with a storage sack but a large cotton sack will do fine.