Patagonia R4 is the warmest fleece they offer. This ultra-warm and windproof fleece material is 137% more windproof than the standard windproof fleece according to Patagonia. The R4 fleece jackets can be worn alone or with a shell for some serious warmth. I think people that keep cacti in their houses are doing so just to prove that they can keep some sort of living thing alive; regardless if it's the heartiest, most self-sustaining living thing on the planet. That thing can survive in some of the harshest conditions on the planet, congratulations.
Patagonia makes a women's R4 fleece jacket and a men's R4 fleece jacket. These cozy fleeces have all the trimmings without sacrificing weight or bulkiness. Sonic-welded seam construction with reinforced stitch (patent pending) reduces seam bulk on center front zippers and pockets. Patagonia has seriously pulled out all the stops on this fantastically cozy R4 fleece.
If you can't quite make the commitment to the standard R4 fleece jacket, Patagonia offers a men's lightweight R4 and a women's lightweight R4. Instead of an interior of R2 fleece, like the original R4, the lightweight has an R1 interior. Not too worry, this fleece jacket still has the awesome sonic-welded seams. This fleece is still windproof and still has great moisture-wicking properties.