The base layer and a must buy more your next camping trip. Groundsheets provide a waterproof layer. between the ground and your sleeping bag. If your tent doesn't have a fully sewn-in groundsheet. you will usually find that the inner tent will still have its own sewn-in groundsheet. Additional groundsheets can still be purchased to cover the full footprint of the tent. Some tents. usually single skin tents may come with a sewn in groundsheet. We still recommend using a separate tailored groundsheet. to protect the bottom of the tent. and stop the sewn-in groundsheet from getting dirty. This makes packing down quick and easy. as the additional groundsheet can be packed away and wiped clean when you get home. rather then having to take home a muddy tent to clean it afterwards.