The groundsheet is an important part of a tent. Groundsheets largely determine how wind, cold weather, water and vermin can be kept out of the tent. With family tents, a full tub groundsheet is the actual norm. The ground sheet of the tent is then fully zipped or stitched in the tent and forms a permanent connection with the flysheet.
The ground sheet also plays an increasingly important role with lightweight tents. A separate groundsheet is often an extra accessory for a lightweight tent. It is usually directly attached to the poles so that you set it up directly with the tent as a fixed part.
With lightweight trekking tents, but also with lightweight family tents and inflation tents, the weight of the groundsheet must be as low as possible. Polyester groundsheets are very lightweight and are the best choice for the lightweight tents. The PU coating of these groundsheets can carry a high water column and makes them waterproof.
For groundsheets of family tents weight is less important. Therefor polyethylene groundsheets are an economical choice. A PVC groundsheet is stronger and of higher quality for family tents where weight and pack size do not matter.