Two years ago, I made a waterproof, padded camera bag out of an Exped XXS rolltop stuff sack and a piece of sleeping mat foam. It’s been a brilliant bit of gear to protect my camera from rain and from knocks. However, it is a little on the bulky side to fit into my Inov-8 Race Pro 4 belt pack. So I decided to replace the 7mm foam with 3mm foam, shown below. The blue is 7mm and the grey/green is 3mm foam, shown with the Exped rolltop bag on the left.
The 3mm foam makes an appreciably slimmer package. Clearly it’s not quite as protective, but I think it will be enough to protect the camera (Lumix TZ5) from being damaged if dropped. I’ve cut the corners off the foam, as it makes it easier to fold the roll top down. Very simple, but very effective.