After some research on hammocks, the thing that stood out is that they aren't all that light. A complete hammock system has a few more components than a Spartan ground camping system, with the hammock and suspension leading the pack. Tarps tend to be larger than solo ground versions, with many in the 10'x12' size. Bottom insulation can add up, with high loft quilts adding as much or more weight as the hammock itself. Like any gear, there are those offerings that are feature laden and use heavy "bombproof" materials. There is a safety factor to consider, and that influences design and materials I'm sure. If you get freaky light with a tarp shelter you might have a bad night, but go too far with a hammock and you may find yourself dumped on the rocks.
My off the shelf Hennessy was 44oz, including the "complimentary" 42" tree straps that are 3oz/pair. That's not terrible for a double-wall shelter, but an anchor compared to my 11oz SMD Gatewood Cape. The Gatewood has no insect screen, so we can add 8oz for a Serenity Net Tent. The Hennessy uses 2 stakes vs 6 on the Gatewood. My sinfully heavy MSR Groundhog stakes are 0.5oz each. The Gatewood does require a pole, and I normally use a trekking pole, but for apples and apples comparison, lets throw in an SMD pole at 2.4 oz. The Gatewood doubles as rain gear, but I'm going to sidestep that.
So the Hennessy is 45oz and the Gatewood is 24.4oz. I'm assuming that we can use the same quilt or sleeping bag in either. The Gatewood requires a pad of some sort and the Hennessy needs an insulation system of some sort. Hennessy offers the SuperShelter with an under cover and a open cell pad at 16oz. The SuperShelter requires a space blanket so I'll add 2.5oz. For apples and apples comparison, I think a Z-lite pad is fair to use with the Gatewood, adding 15oz. I should note that the SuperShelter is offered for 4 season use, with no temperature guidelines. To be fair, the Gatewood is a 3 season shelter, and also has no temperature rating (including the Z-Lite)
So I have 63.5oz for the Hennessy and 39.4oz for the Gatewood. Of course the Expedition is not the lightest Hennessy offering and the Gatewood should have some differential for multiple use as rain gear. A comparable silylon poncho is about 7oz. And my example with the Gatewood is not the Spartan mode, where I would use a shorter pad, a polycro ground sheet, my trekking pole for support and a head net rather than the Serenity net. Discounting the rain gear weight and going Spartan mode, the SMD is down to 4oz for the rain-gear discounted shelter, 1.5oz for ground sheet, 3oz for stakes, 11oz for a short Prolite pad, and lets say 1.3oz for a head net, for a total of 20.8oz. I could shave a bit more using Ti stakes.
The lightest Hennessy is the Hyperlight at 25oz, plus 3oz for straps, 1oz for stakes and 18.5oz for bottom insulation, for a total of 47.5oz. It does have a 200 pound weight limit. It's not bad when you consider the comfort level, with complete bug protection, bottom insulation, and a sleep surface comfort equal or better than a much heavier pad than the Z-Lite and will never got flat from a puncture.
So what would an ultralight hammock system look like? A Grand Trunk Nano 7 hammock is 7oz. It needs a suspension system, so I'll add whoopie slings at 1.4oz/pair. Long 1" polyester tree straps are 4oz/pair. We have to connect the whoopie slings to the tree straps and toggles are probably the lightest means; I'll be generous at 0.5oz for two arrow shaft sections. I like carbiners myself and two Camp Nano biners are 1.8oz. We need a tarp overhead and I'm conflicted about what size to add to this freaky light system; I'm going to go with the ZPacks Cuben hammock tarp at 5oz. We need 1oz of guy lines and 1.2oz for Ti stakes. I would add a ridge line at 1oz. Insect protection is an option; to get UL, I think you need to go DIY, but I'll throw in Warbonnet's bug net at 7.5oz; you could go with a 1.3oz headnet to be truly freaky light. We're up to 28.6oz so far with the heavier bug net.
And now for my favorite part, bottom insulation. Fact: you aren't going to sleep in a hammock without some sort of insulation when the ambient temperature is below 70F. I don't like this part of hammock marketing; it all seems patched together for the most part. Clark is the one manufacturer that stands out with a well coordinated insulation system, but Clark and ultralight don't match. Hennessy has taken their shot at it with the SuperShelter at 16oz.
If you have an idea of using a standard 20" pad, forget it; it won't have enough side coverage and it feels bad. IMHO, pads used in the hammock completely detract from the best parts of the hammock experience. If you must, there is the Segmented Pad Extender, once made by Speer Hammocks, that was a nylon sleeve that used a 20" pad in the center and 5"x20" pads in side pockets to wrap around you and insulate your shoulders and hips. I have one and I'm not impressed. Some hammock campers use the 24" Walmart blue CCF pads, which I don't like, but YMMV.
So we get to under quilts, with much of the same construction and filler variables you see with sleeping quilts and bags and it's the old choices of synthetic vs. down and how-cold-do-you-want-to-go. Under quilts come in a variety of lengths too, so there are a lot of choices. Suspension systems are typical some sort of fore-and-aft shock cords that support the upped edge of the under quilt and allow some adjustment. I'm going to go with 16oz for a good 3-season down underquilt.
I developed an under cover or weather sheild made of silnylon that doubles as a hoodless poncho. It is 9.7oz with the shock cord and toggle suspension and the stuff sack. I am experimenting with various insulation packages to go inside, always with the knowledge that I can awlays drop $200 or so on an under quilt and be done with it. I have made a 48"x60" insulation pad using an AMK HeatSheet space blanket and 1/2" batt of very pedestrian polyester fill that is 11oz. It mates very well with the poncho under cover and cost $15 to make. Just using a space blanket with the under cover helps in cool 50F-ish weather. I am looking at the Molly Mac Gear Insultex pad, the Hennessy open cell foam pad that comes with the SuperShelter, or making my own Insultex insert for the under cover. If I get brave and dive into sewing, I'll have to try making a synthetic underquilt.
So we have 28.6oz with the "heavy" insect shield. Add the 16oz under quilt and we have 44.6oz for a complete and viable UL hammock system with a 300 pound rating.
Here's the breakdown on my dream system:
Warbonnet 1.7 Traveller hammock with suspension: 16.5oz, $60 (250 pound weight limit)
Warbonnet bug net: 7.5oz, $65
Zpacks Cuben hammock tarp: 5oz, $235
50' 1.5mm Zline, 0.88oz, $12.95
Six Ti stakes, 1.2oz, $15
Te-Wa Freeze 3-season underquilt (20F): 14oz, $189
Total weight: 45.08oz, $576.95
That's under 3 pounds for a large shelter, insect protection, and the eqivelant of a VERY comfortable sleeping pad and good to 20F. It can be lightened a bit using a head net instead of the bug net, or using a DIY bug sock. The cost can be reduced by using a silnylon tarp and/or DIY insulation, or a 24" Wally World blue foam pad if you can stand it.