Find Gewa felts to be thinner and less dense than others on Thomann, but more durable and less prone to wearing/breaking down into powder.
As a rough guide the grey fibre felts tend to have larger more durable fibres which are easier to put on and off and don't really break down, they only snag and pull to fluff occasionally. The black ones tend to be much stiffer, firm and harder to work, but more brittle/fragile fibres which turn into powder as they crush down with usage.