Rating: 5 / 5
In a sense, every Nunatak topbag/quilt is custom to one degree or another (if one is taking full advantage of Nunatak's services). Mine is no exception, being made for my height and with some local adjustments made to the girth of the quilt body and foot box. as well as to baffle height and fill.
In general, the Arc Specialist (http://www.nunatakusa.com/Sleeping_Bag_Arc_Specialist.htm) is a further development of the Arc quilt originally made to BPL's specifications and sold exclusively by them a couple of years ago (http://www.backpackinglight.com/cgi-bin/backpackinglight/arc_x_variable_girth_down_sleeping_bag.html). It has 3 adjusting straps underneath to create a 'variable girth" system that adjusts to both conditions and the amount of additional clothing (insulated layers, for example) the sleeper wears under the quilt. It has a well baffled foot box. Baffle spacing is 5' and baffle height stock (remember this is for single layer--not total loft of the quilt) is 1.75" ( mine is 2")---this equals excellant control of the distribution of the fill. There is a choice of shell material but I elected to use Pertex Quantum for it's downproof, water resistant, high breathability and lightweight charateristics. *800+" fill power down is used---this seems to translate to the quality level of the down used by most high end bag manufacturers. With 9 oz. of down fill, my Specialist weighs in at just a hair over 16 oz. after trimming of the generous amounts of strap material which comes with each Arc quilt. The quilt comes with a suggested temp. rating of 32 degrees F.----mileage will vary, as they say. My custom modifications make it a little warmer (smaller volume, a little more fill, slightly taller baffles).
Quality levels and custom mods are well worth the wait (and I think expense---this is a small volume cottage firm). Design is more sophisicated than it's competition and the Ray-Way quilt kits and this results in a lighter and more efficient quilt.
This is the core of my go-to SUL sleeping system and I'm very pleased with it. A "5+" if this were possible.