Well this is $75 less and lighter. The R4 is 300 weight fleece while the R2 is 200 weight but lacks the chest pocket of the R4. The R2 will be stretchier but the R4 will block wind better (thanks to the Polartec). It depends on what you want to use the jackets for. If you want a midlayer, the R2 is probably better, but if you were hoping for a heavier duty outer fleece, the R4 is your best bet.Update: The questioner is asking about the "Lightweight R4" which is a windproof version of the R2, as far as I can tell, and I have both. The cut is slim, like the R2, and the material is light too, like the R2. So really it's the windproof aspect that's the main difference and this makes a *massive* difference if you're out in the snow or where there's a chilly breeze.It's difficult to say which one you should get as you don't lay out what you want it for, but here is my advice:-R2 - great mid layer, or outer layer in benign weather for high activity. If you're hiking up a hill in spring or fall and it's not raining, this is the fleece I would wear. The Lightweight R4 will quickly get sweaty and you'll be busy venting it the whole time. The Lightweigh R4 is also less packable as the windproof laminate prevents it from squishing together as well as the R2.-Lightweight R4 - walking around your neighborhood in spring or fall and it's a bit windy. OR, you're out snowshoeing in 25F+ weather. Combine this lightweight R4 with an R1 pullover underneath + R2 T-shirt and you'll be toasty but have venting options. Take a down jacket to slip over it when you stop for lunch. The slim cut gives great mobility, and I'm also led to believe it's waterproof due to the windproof laminate, but that's a backup plan, as if this thing gets wet, it gets WET and soggy, and therefore colder.