I can only speak for Hammock Gear, but having a 0° incubator had got me low teens with very warm results. I suspect it could go to zero with no problems, have to start adding insulation below that. Super easy to put up and very flexible in how you can set it. Fits my XLC just fine. Plus you have to consider they (or any of our cottage vendors I'm sure) would customize pretty much anything including over stuffing, and such to increase insulation.