Down poses two challenges: Washing and drying. Let’s start at the beginning.
First of all, leave the washing detergent on the shelf. It’s best to use a detergent especially for down. If you don’t have any, a wool detergent is also suitable. And on the subject of wool, you should also use your washing machine’s wool wash programme.
Once that’s done, turn your attention to drying. Down is stuck together and lumpy after being washed. The best thing to do is put it in the dryer at a low temperature. Even if the item feels dry after it has been in the dryer, always check that there are really no more lumps. If there are, give it a short break then put it back in the dryer for 20 minutes and repeat until all lumps have disappeared. It is better to have spent too much time in the dryer than too little. ;)