How to clean this cap?

[czesio]

How to clean it?
Regards
Szymek

[Paul R.]

That cap is very fragile. DO NOT attempt to clean it. As a conservator I would not even brush off the dirt. leave it as is.

[Will Brown]

Agreed. Somethings are just too far gone to be "restored" in any way... cleaning included.

[Stahlhelm]

Again, cleaning is just not a good idea. You will be dissatisfied far, far more often than you will be satisfied with the results. As Paul said, this cap looks even too fragile to be brushed. I wouldn't mess with it. I'd just be happy it exists at all, and do my best to preserve it as it is.

Chris

[BenVK]

A gentle brushing wouldn't hurt I think.