Sleeping Bags All the sleeping bags in the Louis range are filled with synthetic fibres. This makes them very sturdy and insensitive to moisture. Before buying a sleeping bag, you must decide whether you prefer the "mummy" or "envelope" style. The advantages of the mummy style include weight, pack size and insulation rating. Envelope sleeping bags, on the other hand, offer greater freedom of movement and can be opened out and used as a blanket. You should check the maximum user height stated! Louis has the Starter XXL for taller than average people.