Many cordless vacuums don’t have brush bars, and those that do only contain nylon bristles. While these loosen dirt from carpets, they’re not as effective on hard floors where fine dust can be left behind.
The brush bars of Dyson cordless vacuums are different. They have a row of anti-static carbon fibre filaments, as well as nylon bristles. The filaments prevent the build-up of the static charge that holds the dust to the floor, allowing it to be sucked up into the vacuum.