Stolen from Automobile Mag:
How To Wash And Clean -- Safely
Compared to glossy paint finishes, the surfaces of matte cars need to be washed more often and more gently. The most important step is to avoid creating scratches or swirl marks while washing. That means buying high-quality microfiber towels and soft wash mitts, and washing them thoroughly after each car wash. Any type of automotive-specific liquid car wash soap can be used safely. Owners also should use two buckets -- one with soapy suds, one with just water -- to avoid contamination. After applying soapy water to the car, dousing the wash mitt in the plain water and wringing it out will prevent some grime from being carried back into the clean, soap-filled bucket.
"We preach the two-bucket method on a gloss finish, but it's almost mandatory on a matte finish," Pennington says.
To avoid introducing corrosive and scratching brake dust into the paintwork, owners should also use a separate wash mitt for cleaning the wheels, and should do so with a separate bucket of water.Hyundai, meanwhile, recommends beginning each wash session by pressure-washing the car. The nozzle should be at least 10 inches from the surface of the car. After that, Hyundai suggests using the same two-bucket wash method advocated by Meguiar's.
Both BMW and Mercedes stress that anything that sticks to the paint surface, like dead bugs, tree sap, or bird droppings, should be removed immediately. Because rubbing aggressively can ruin the matte finish, the companies recommend dousing the item in insect remover or car-wash soap before gently rubbing it away. The key, Pennington says, is to avoid excessive friction when trying to remove anything stuck to the paint surface. Water spots should likewise be cleaned off quickly, even if they result from something as trivial as driving past a garden sprinkler.
As waxes and polishes are verboten, Pennington advises adding some UV protection and shine to matte paint with specially formulated spray waxes. Meguiar's own Ultimate Quick Wax, for instance, doesn't have any harsh cleaners that will damage matte paints, and it creates a protective coating over the paint surface.
Flat Finish: How You Should Tend To Matte Automotive Paint