Flame resistant? No, not really. I once had an RCAF intermediate flight jacket in poly/cotton that I used before I got my hands on a Ventile jacket. I burned a hole in it with a cigarette. (The Ventile is no more, but that's a different story)
It WILL melt and burn because of the polyester. It's a little bit funny that the CF's flight gear was never made of Nomex flame retardent fabrics until just a couple of years ago.
I will say this though: A properly treated poly/cotton jacket will be extremely water repellent and is not a bad substitute for Ventile. The big secret is in the twill weave, it has a very high surface tension. That means that water droplets are less likely to soak in on contact such as with Ventile, which is an oxford weave. The problem with twill woven fabrics is that eventually water will start to soak through but due to the nature of the weave, the fabric cannot swell in a uniform pattern. And as we all know, that swelling is what makes Ventile such an amazing fabric.
To summarize: Yes, poly/cotton will melt and burn. But it's a lot cheaper than Ventile and given a good proofing will keep you dry for quite some time.
Adam
