I have wind tunnel U6485900 self-propelled. They stopped making self-propelled vacuums many years ago, before there were pressure systems, but I have to keep this vacuum as I have issues that make it very difficult to use non-self-propelled vacuums. As with all self propelled wind tunnel units they tend to let air escape around the hole where the bag attaches to the unit, unlike many other bags this one has some sort of gasket, what a great idea! It's also HEPA and cloth, those things help keep the air cleaner when vacuuming. There are some that are a little cheaper but are worth a few bucks more for great features and quality.