For our units, we chose this recyclable EPP foam because it is very resistant to stains and marks. A really good idea to leave this toy to the children in complete peace of mind. But if ever your units need a little clean-up, a refresh, then it's possible and not very complicated, you'll see: a little hot water, a bit of soft soap, a cloth, a sponge (no no, not the scratchy side) or a soft brush, and that's it. It shines like a new penny (very old expression it's true... we got a little lost...). Others who use the same material even invite you to put it in the dishwasher without fear. That's how resistant and waterproof it is. We will not do the same, for the good and simple reason that we have for our part plugs with magnets (the very principle of our toy) and that we want to pamper these precious parts to preserve the connectivity. As for the plugs, a wipe with a cloth or a soft brush from time to time, with the same soft soap used above, to clean the traces and remove the light layer of dust and you will be as good as new (we removed the "penny" this time !)