Here are some more in depth instructions on the process for spray painting plastic.
If your helmet is glossy (POC helmet style) or you just want to make a helmet a different color (as in blue to yellow) you will need:
sponge + soapy water
sandpaper (coarse not fine)
Painters tape or masking tape
Lots of newspaper
spray primer for plastic (krylon makes a good one)
acrylic spray paint or spray paint for plastic
(optional) spray polyurethane coating
Also note that most spray paints for plastic are glossy and not matte. So if you want matte you will need to use a plastic primer and an acrylic paint.
OK! YOU ARE READY TO START
1. Remove as much of the helmet padding and liner as you can (like on bern helmets you can pretty much take off all the parts.
2. Clean the helmet surface with soap and water. Make sure to get off all the dirt.
3. Let it AIR dry. Towel drying will not get it dry enough.
4. Take the sandpaper and rough up the surface. The less smooth the surface the more likely the paint will take to it. (I have had the best results with bern helmets once again).
5. Using the tape and newspaper mask off all parts of the helmet you do not want painted. (Straps, liner, ear pads, etc.
6. Lay down some newspaper for a drying space.
7. Ok here is where things can be simple or more complicated:
If you are looking at making a a colored helmet black or white you can just prime it or paint it with the plastic specific spray paint. If you are doing this skip to the next step.
If you are looking at changing the color of the helmet (as I said before blue to green) you will need to do all these next steps.
Spray the helmet with the primer. You will only need one good coating of primer. Let the primer get dry to the touch.
8. Next take whichever color spray paint you want (blaze orange is a personal favorite) and apply a first light coat. Let it dry to the touch.
9. Second coat time! Let it dry for a couple hours more than usual.
10. If you want a matte finish this will be the end of your process. You will probably need to touch up the helmet every once in a while as it gets dings and the primer will show through. The primer should hold so you can just touch up with the leftover paint.
10B. If you want a glossy finish you will need some spray polyurethane they come in a bunch of finishes from satin (semi gloss) to high gloss (shiny shit). Do two light coats letting them dry between coats and you are done.
If anything is confusing lemme know.