So I've been a long time reader here but this would be my first post, so go easy on me if this has been discussed to death (despite an exhaustive search that turned up diddly) or if this is the wrong place for the post.
For quite some time now I've been toying with the idea of one piece of sleeping insulation gear that can be used in multiple scenarios. For example, something that can be used as an underquilt, or taken off and zipped up as a sleeping bag when a hang is not appropriate. My wife and I do a lot of backpacking and camping together so I would like something with opposite zippers so the two "bags" can be zipped together and thrown on an air mattress for a queen size sleeping bag. These three requirements are what i'm primarily after but if it was at all possible to go one step further and separate the underquilt and configure it as a top quilt for use with a ground pad that would be even better, but this is probably the least used sleeping arrangement, so if it over complicates things it'll be the first to go.
I'm looking to use 850fp hydrophobic goose down, i'm 6'4 and my wife 5'10 and I need these "bags" to be ~15 deg. This adds up to a lot of down approx $500-$600 worth, the high cost is partly why I don't want to make separate bags and quilts for each individual scenario. Has anyone seen such a design that's still effective as both an underquilt and a sleeping bag? I've seen a few on amazon and such but the designs look terrible. I haven't used an underquilt with my hammock just yet (we live in Texas and it just hasn't gotten cold enough on a trip yet to need it) but my wife and I are planning a 9 day BP trip through rocky mountain NP for 2020 and it will be necessary then. Thus, i'm not sure exactly how my wife or I would like it set up, however I figured the fabric is significantly cheaper than the down so if i don't like the design or configuration I can always start over with new fabric and just re-use the fill. My wife and I are avid DIY'ers and have a number of sewing projects from hammocks to garments under our belts so i'm fairly confident we can handle such a task.
As for the design....
Since these would be used for backpacking weight and pack size is a bit of a concern, however we are currently packing old 5lb & 5.5lb synthetic fill 30 deg bags so just about anything would be lighter than this. My "bag" will get used about 60% of the time as a sleeping bag while my wife's will be used more as an underquilt. Since I would like these to zip together for a queen size double sleeping bag they would need to be the same length, and also width since our hammocks are both the same width. This being said, i'm looking at an 80" x 72" rectangle with ~2-2.5" tall baffle & 10-15% over stuff. I'm thinking two separating zippers, one for the long side and then one 36" long for the foot end the would be zipped only in the sleeping bag configuration. On the foot and head end, is a sewn channel with an adjustable elastic chord running through (this would be below the zipper on the foot end), the elastic would be wrapped around the ends of the hammock and adjusted to control airflow. Sewn to the channel would be a series of buttons to allow for a clew to be set up in the underquilt configuration. I would also include a removable hood that can be zippered on for sleeping bag, or removed and worn independently in a hammock.
I've been using the calculator provided by CatSplat, Provided by https://ripstopbytheroll.zendesk.com...my-underquilt- which gets me approx 15 degrees with a 2.25" baffle height and around 30oz total weight (i'm expecting more like 40oz once the zippers and cordage are added in). However, this is just a reference guide so can anyone validate its accuracy with regards to temperature rating? It looks like its assuming just a modified rectangular baffle design, which i don't plan to use.
As for materials, I tend to sleep pretty warm and may sweat a bit while my wife is just the opposite. So I will need something very breathable and soft for the inner shell and my wife something still soft but maybe a bit less breathable. I'm not sure which would be better, Nylon or Polyester based, but i'm considering Argon 67/90 or Ion from dutch or HyperD or one of the Membrane products from RipstopByTheRoll. can anyone speak to these materials for their softness & breath-ability? For the outer shell, i'm considering something a little heavier to handle the wear and tear, possibly Argon 90? Ideally i'd like something that can be waterproofed around the ends or at least shed water fairly well. For the baffle wall materials, i'm going as light as possible, probably a 0.5oz noseeum.
I realize this is a'lot of questions for one post but what can I say, its my first quilt and i want to get it right! thanks in advance for any help / insight!
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