Paint "protective varnish" on styrofoam, that withstands weather.

[nattugglan11]

I have a nice new bike helmet, but its lower part is not covered with plastic, instead "bare" molded polystyrene. The helmet will take some wear and tear over time as it will be packed in and out of a backpack every day, etc. I'm considering applying some paint or varnish on the surface to make it last a bit longer. Thinking matte boat varnish spontaneously, as it is thicker, but I'm not sure if it adheres to plastics. Any other tips? (varnish that withstands rain and adheres to plastic)

There are other helmets but extremely few that fit well on my large head The helmet was expensive so I don't want to buy a new one too often.

 

[Bo arnold]

Do not paint with boat varnish, it can probably damage the Styrofoam; paint with solvents should be avoided; paint with a water-based woodwork paint that does not harm the Styrofoam.