Earlier this year I picked up the Wiggy's sleeping bag and the made-in-the-USA vapor barrier the Rivendell sells. Being a relative newbie to camping, I was not familiar with the vapor barrier strategy, but the science (as explained by Grant) seemed to make sense. And, my camping is mainly 3-season, which in North Carolina is more like 2-season in much of the country. In other words, the Wiggy, rated at 45 degrees will probably be good for 90% or more of my camping.
I was right. After seven months of owning my set, last night was the first time I have had a chance to use the vapor barrier. It was a pleasant day yesterday, but the forecast low for our weekend excursion was upper 30's, the sweet spot for the bag/vb/tent combo, according to Rivendell.
The Riv recommends wearing just a thin layer of wool inside the vb. Its important, sayeth Grant, to fight the urge to overdress, as too much clothing will turn you into a sweaty mess. I don't have the wool, but I do have modern synthetic base layers, so that's what I went with - REI long underwear pants, a capilene shirt and fleece socks. In lieu of actual hair, I was sporting my Walz capa RUSA hat.
The results were pretty good. I'm generally a cold sleeper, but the prescribed combo kept me warm enough to sleep until about 5a when the temps started falling through the 30's. I was able to sleep another hour, but then I was uncomfortable enough to be tossing and turning looking for some warmth.
Some relatively modest changes would've made it work for me. I have a fleece sleeping bag liner that would've given me the few extra degrees I needed, but I'd given it to my son. Some heavier fleece socks would've been better, but I chose not to pack them. And my cycling tights would also probably be effective at adding a few extra degrees as well.
All in all, though, the bag and vapor barrier delivered as advertised and I imagine they'll work to the mid-30's for most folks. The forecast for tonight is ten degrees warmer, so I'll give it a go with the same garb. Should be perfect.