Disposable Lens Brush
From Rollei Mailing List;
No, these are hard vacuum coatings, probably made of Magnesium flouride, which is fairly hard. I am not sure what "extremely careful" means, I would be careful of any lens. Some optical glass is pretty soft and coatings are softer than some glass. Cleaning should be done with the object of keeping grit of any sort from getting trapped and rubbed against the glass.
Tissue used for cleaning should be used once and discarded. I don't like the use of lens brushes, which an pick up grit and scratch the next time they are used, a one-time brush can be made of lens tissue by rolling into a tube, tearing the end and folding the torn ends so they face the same way. Use this once and toss it.
Some lenses I've seen look like
they were scrubbed with a pad of steel wool.