My enlightened equipment enigma is made right here in mn and ppl are always shocked at its weight
Nunatak makes a center zip in whatever spec you want. I can think of that one right off hand lol.At zero degrees, you’ll be carrying a lot of extra weight (but even more bothersome than that to me is the extra volume in the pack as lofty 800+ fill power down bags pack down much much smaller) if you don’t choose down and if you don’t choose a mummy. Some of the wide Western Mountaineering bags give you a lot of freedom to move around even though they are mummy style. The Sequoia is built with tons of room. However, if you don’t fill the space, the sleeping bag will be less efficient as there is excess air/space to heat.
Off hand, I can’t think of a made-in-USA front zip that will take you down to zero.
You call and talk to Jan and he'll make whatever you want. Those spec charts are just starting points. Will it be cheap? Nope. He does a lot of custom work. You can even get a zero degree Raku wearable bag. The only thing limiting what you get from those guys would be your budget, and good gear is never cheap.Looks like their standard is 28 and 18 degrees F. To make a 0 degree bag, they would have to create a different design with thicker baffling and larger outer shell. Or severely overstuff the 18 degree bag which is not efficient use of down loft. There is a limit to what you can do with a center zip. At a certain point (probably 15 degree rating), you need to design a neck baffle to trap heat. I guess you can slum it and us a down jacket wrapped around your neck . The North Face Inferno is built for cold but who wants to buy made in Asia and support the big corporation?