We've had this mattress for a while and thought it would be a good time to remove the cover and wash it. It's a hefty bit of kit, but we have a large machine that will take a 9kg wash so we thought it would be fine. It washed. But there was no way the fabric was ever going to get the water out, we respun it, we squeezed it, left it to drip dry, and after four days it has finally dried. My wife also tried emailing the Dormeo company for advice, only to be told that they don't sell those mattresses, and we must have bought it from somewhere else.
So, be careful, best washed in a laundrette.
After saying all that it IS a very comfortable mattress and made a big difference to my comfort.