After painting the armor, we need to coat it with "Dull cote" lacquer. Testors got one but the local saler have no idea when I ask for one.
I've found another stuff at a paint shop. It's called "Matt PU". The shop assitant also tell me the formular :
" 3*Matt PU + 1*hardener + thinner "
And this lacquer will be detroyed after 5 hours if you don't use it.
I'm wonder what is the different between "Testor's dull cote" and "matt PU". Should I try it on my armor?
Thank you for your attention.

My guess is that PU stands for polyurethane. AFAIK polyurethane paints are more resins than lacquers (that's why there is hardener needed). They are used for e.g. model race cars, because they are very tough and quite flexible, what means they survive crashes and don't flake off the surface when car bodies are deformed. But I'm not sure if polyurethane paints are safe for styrene plastic and for model paints. They may be too agressive for them, but I really don't know.

Pawel

Thank you, Mr. Vodnik
I've tested this stuff on one of my armors. It's good. By the way, they don't sell "Testor's Dull cote" in my city.