jjcanoeguide wrote on Mar 1^st, 2010 at 5:37pm:

I recommend buying a jacket at least 1 size larger than you think in order to fit your PFD INSIDE it.  You’d be amazed at how toasty warm a rain jacket can be with your PFD serving as insulation.

Same idea except I prefer to wear the PFD on the outside. Stiil get the benefit of more insulation and you can remove it easier when it's too warm. Also helps to shed water away from torso. My old goretex leaks at the seams given enough time in the rain and the PFD solves that problem. Most PFD's are easily adjusted to fit over a variety of clothes.