The M65 jacket was a staple of the US armed forces from its birth in the jungles of Vietnam in 1965 right through to the late eighties. The jacket is a polyester cotton mix, with a tight weave and a DWR (durable water repellent) treatment on the surface. The Soviet TTsKO jacket is made out of the same material, and let's not forget - both jackets are MILITARY items, and no military would let their soldiers use jackets that go to "drenched" after 1 minute 30 seconds of rainfall exposure (as they perform in DayZ).

I own a jacket like this, and it is rather reliable in heavy rainfall for extended periods of time. However, one does get soggy after a while. In game, it would correspond to "damp" (and only after 30+ minutes of cumulative exposure to rainfall) without progression to "wet", "soaked" or "drenched".