Mid 2012 I bought a Rab Neutrino SL 200 sleeping bag. To recap, this is a top bag with virtually all of the insulation on the top of the bag. The underside has some insulation underneath your legs, Primaloft 100, but none under your torso. The idea is that any down underneath your body provides next to no insulation and therefore is superfluous.
Unfortunately, I’ve never quite got on with this sleeping bag. Even with a good sleeping mat, I found it a bit cold on the underside. I was thinking of selling it. However, I had a brainwave. Why not add a slab of synthetic insulation in the sleeve where there’s no insulation?
Initially, I thought of a DIY solution of adding some fleece. Then I thought of adding something like Primaloft. As this would be beyond my abilities, I contacted Marco at As Tucas. He uses Climashield APEX insulation for his quilt, which is similar to Primaloft. After an exchange of emails, I’m getting him to use APEX 167 which is heavier grade than the Primaloft 100.
Synthetic insulation should be a bit warmer than down when compressed and turn the bag into a decent 3 season sleeping bag. Marco reckons it will add less than 100g to the weight (80-90g?), which would take the total weight to less than 673g. For comparison, my Pipedream 400 is 740g.
It’s possible that the Neutrino might be even warmer than the Pipedream as the down quality is higher and it has as much down on the top side of the bag. Hopefully the synthetic insulation will be warmer below my body and I will be able to dispense with a sleeping mat cover. If so, the total weight saving could be around 200g. How much will it cost? £33 plus postage costs.
I think it’s worth a punt, so I’ve posted my bag to Marco today. It will be an interesting experiment. I’m surprised that there aren’t hybrid sleeping bags with synthetic insulation on the underside, or at least, I’ve not seen any.