I haven't kept track of R values for my pads but can say by observation that it depends on how you sleep. I use and old ensolite pad underneath a thermarest trail lite ( 1 1/2" withno cut outs in the foam) and am fine down below 0F. If I take less, I get cold, yet I've been out with friends who will comfortably sleep in the same conditions on just a 1" thermarest lite with the die cuts. See if you can find an older thermarest or borrow one and use it with your ridgerest. If you find you really like winter camping then go for a Down Airmat 7 or 9 from Exped.