A rope bag is just a bag to store your rope in. However, a canyoneering rope bag has several design features that make it very useful. There are several different distributors for canyoneering rope bags.
A good rope bag has:
The easiest way to stuff a rope bag is:
When should you use a rope bag and when should you just coil the rope? My personal preference is to coil any rope shorter than 120 feet and bag any rope longer than 120 feet.
A rope bag is very useful for keeping your rope tangle free. You can hold one end of the rope and throw the bag off a cliff and the rope almost always comes out without major tangles. It's also useful for when you only need to use part of a long rope because the unused portion stays in your bag.
A rope bag adds extra weight and bulk to your pack.