How to wash (and dry) a foam mattress

a) After drying a few hours the mattress is dry on the surface but still wet inside.
b) After rolling it tightly and mangling it (walking on it with your heels) the water gets evenly distributed, which allows the surface to dry again.

Actually it is the drying of the mattress that is the problem (washing it is just like washing anything else, you just need a bigger container).

After leaving it to dry for a couple of hours it will feel dry on the surface, but if you squeeze it hard, you will notice that it is still wet inside.

If you do like when you're drying other stuff: wait longer, and longer, you will just discover that it begins to smell after like 2 weeks (still being wet inside)

What one should realize is that it is only water close to the surface that will evaporate (water needs contact with circulating air to evaporate).

So what one should do after the mattress has dried for a few hours is to roll it up tightly, and then walk on it with your heels so that the water gets redistributed evenly, the mattress will feel wet again which is good because that surface water will now have a chance to evaporate.

Then you have to do this preferably once every few hours, (or at least once in the morning and once in the evening), and you will notice that it gets dryer and dryer for each time. It will still take several days but hopefully not so long that the water begins to smell.

To further help on soaking up water, you can roll in a dry sheet or towel or something, especially in the beginning when there is lots of water that can be soaked up.