News flash! The 4-Season system has recently been tested by British Commandos in Norway above the Arctic Circle. Here's the review:

A TEST OF THE HENNESSY HAMMOCK IN AN EXTREME COLD WEATHER ENVIRONMENT
PROBABLY THE ONLY HAMMOCK NORTH OF THE ARCTIC CIRCLE
a Review by Ben Reynolds

It’s indisputable.  Hennessy Hammocks could well be the best in the world.  Light, durable, comfortable and excellently engineered… perfect for warmer areas of the world, right?  Well, you will have seen from the website that ever evolving design solutions are attempting to expand the boundaries of the hammock inhabitable world, from calm low lying areas and comfortable lower latitudes, to where the silent killer reigns supreme…. cold.   So, it was with Hennessy Hammock’s Explorer Ultralite Asym, along with elements of the insulated Superstructure that I found myself in Northern Norway in order to test whether the cold can be defeated by this intruder from the tropics. 
 
 THE TEST
 
CONDITIONS.  The system was tested in the area of 68º 33’ 37.12’’N by 16º 58’.54’’E, east of Harstad, Norway.  Initially mild temperatures prevailed, fluctuating around freezing, which resulted in freezing rain, sleet and snow.  Though this is not the extreme cold that was later encountered, it was far more testing due to the freeze-thaw effect and moisture content of the air which accentuated the cold.  Minimum temperature encountered was - 18ºC (0ºF) still air and estimated at -30ºC (-54ºF) with wind chill.  Maximum precipitation encountered was 7.5cm (3 inches) of snow in 6 hrs. Click here to read the entire review.

...CONCLUSION.  The Hennessy Hammock insulation system is capable of supporting a lone traveller in extreme cold weather environments down to -12ºC (10ºF) in the format tested.  This was dependent on the sleeping bag used and a bag with a lower comfort zone than that used in the test will similarly reduce the -12ºC figure.  This figure will also be reduced by: (1) adding insulation to the Under Cover e.g. spare clothing/suitable vegetation, (2) use of the Over Cover, and (3) a solution to cooking which would also heat the living space...However, for those comfortable operating in extreme cold the system works in all respects other than the method in which one can cook, but there must be solutions out there. 

Thanks to Ben for his detailed and informative review!

Letter from SuperShelter User

Tom.

I was given the SuperShelter system a year ago as a gift and it is the best. For starters your customer service is number one. I had some issues setting it up the first time out. Yea I should have done it in the back yard but just winged it. I called your company with my cell on the trail. I ws shocked when you called me back within 15 minutes personally and explained what I was doing wrong. I had no more problems. After more than a year of heavy use it held up great. Going to order a new underpad before next winter. Considering the use and abuse of my Explorer Deluxe and the SuperShelter system it has proven extremely durable but everything has limits. I am very hard on gear and have owned my hammock for two years now sleeping inside the thing for weeks on end. The system alone keeps me cold-back-free down to about 35. Toss in my jacket and sometimes a poncho linr and I have taken single digits with a proper sleeping bag. But that is just me. Everyone is different. Once weathered a heavy snowstorm inside my SuperShelter. The wind proof bottom cuts the wind chill perfectly. Even in the summer I use the silnylon bottom. Keeps the bugs off the bottom of the hammock.

The overall comfort of the hammock is outstanding and I just want to thank you personally for making such a great product and your fantastic customer service. Thanks again for those hammock camping tips. They came in useful. Sincerely, Kevin Renkavinsky

"Total Satisfaction!"

I purchased my first Hennessy Safari Asym Hammock back in January of this year. Living in South Carolina, I had several opportunities to use it in February and March when the weather was not too cold (i.e lower than freezing). Total Satisfaction!  Seem to remember many vows of never sleeping in a tent again during those initial nights.  However, several weeks ago, I decided to give it a try on a backpacking trip with the Boy Scouts.  Being the CubMaster for the Pack associated with the Troop, the Boy Scouts needed some additional adult leaders for their "most strenuious backpacking trip of the year" up Mt. Mitchell in North Carolina.  During the second night of our trip, at an elevation of 6,000 feet, we were hit with what was supposed to be a "potential light dusting of snow".  That night, I experienced first hand how this hammock holds up in extreme conditions to include 30-40 mph winds, rain, sleet, between 6-12" of snow, and temperatures of 5 degrees F with windchill.  Surprisingly - Total Satisfaction!  Other than what one might call "periods of excessive rocking", I stayed relatively dry and warm!

I used my North Face bag rated at 20 degrees with a Thermarest RidgeRest foam pad.  I slept in a pair of  milano wool thermals.  As the sleet started coming down, I decided to experiment with using an old military issue solar blanket.  I placed it under my foam pad and wrapped it completely around my sleeping bag.  This kept me nice and toasty.  Unfortunately, the outside of my sleeping did get a little damp from the condensation that was collecting on the foil. 
The downside was I had several adjustments to the rain fly to make throughout the night due to the unexpected high winds and my lack of experience in using the gear.  In addition, in the morning, the half-hitch knots that I used to tie the hammock to the trees were covered in ice and frozen solid.  I poured the last of my hot morning coffee to melt the ice and loosen the knots.  After that, I had the entire hammock balled up in my pack within 2 minutes.
Given the weather conditions, I slept very well and stayed warm through the night.  On our 8 mile trek out in the snow, I kept hearing comments from the scouts - that they had never seen anyone with a tent hammock before, especially in the snow and how they were going to have to get "one of them hammocks"!  - Jim Towler

Always check your gear before you go!

Always test your gear close to home before you start out on your trip, especially if you're setting our for some cold weather camping. Everyone has a different metabolism (in the winter, some folks sleep with the windows open, some with the heat turned all the way up) and everyone needs to find the right combination of sleeping bag and insulation -reflector pad, closed cell foam pad or car windshield reflector.The hammock fly can be tied down close to the hammock like a tent. Even in the winter, the mosquito netting serves a useful purpose. The fine weave of the mosquito mesh blocks out about 90% of the wind and provides a calm space inside the hammock, even when the fly is not fastened down as low as possible. For winter camping, you should think of polar fleece clothing, mittens, gloves & booties.

Test Results - Winter Camping in Hennessy Hammocks
Hennessy Hammock participated in a gear test with BackpackGearTest  which tested the Ultra Light Backpacker 1.5 Hennessy Hammock and also tested several radiant reflecting materials and other strategies for staying comfortable at low temperatures.

Radiant Reflector Theory (as I understand it)

First you need a radiating heat source which is your body. Opinions differ, but somewhere between 19 and 50 per cent of your body's heat is radiant. Then you need a radiant reflecting surface like highly polished space blanket material or aluminum foil. But most importantly, you also need a dead air space between you and the reflector. This is where those invisible little wiggly red arrows radiate from your body across the dead air space and bounce back off the reflective surface which causes a warming sensation, as if you had some kind of heat source under you. The closer the reflective surface is to your body without touching you, the more efficiently the radiant reflector will work.

Without that dead air space, your body will be directly against the radiant reflector and your body will conduct much of its heat right through the radiant reflector with very little benefit from the reflector.

The First Experiment: Emergency Space Blanket

An emergency space blanket was tested as a lightweight radiant reflector. The most important feature of a space blanket is it's ability to bounce back radiant heat that would normally be lost through the sleeping bag insulation compressed beneath your body. When used inside the hammock. it was found to be extremely noisy whenever the occupant moved. It also had a tendency to shift and was difficult to adjust beneath you. When the space blanket was placed over your sleeping bag in the hammock, large drops of condensation would form on the underside of the space blanket within 3 to 6 hours. When the space blanket was suspended under the hammock, there was much less noise and and no adjustment problems. When the space blanket was adjusted properly and close fitting to avoid drafts, a high percentage of the radiant heat that would normally be lost was reflected back to make the compressed insulation of your sleeping bag even warmer than the uncompressed insulation above you.

The Condensation Factor While the space blanket reflector does a pretty good job of keeping the bottom of the hammock warm and windproof, I still consider the space blanket as emergency equipment only. The downside of this solution is that when warm, moist air surrounding your body contacts the radiant reflector cooled by the lower temperature air moving under the hammock, condensation will occur. For temperatures below 50 degrees, you will probably require additional insulation.

One solution is to flip the space blanket over after a few hours putting the droplets of condensation attached to the space blanket on the outside where they will evaporate in the breeze. The real solution is to put some insulation under the space blanket to minimize condensation and that's covered under hammock Pads in the paragraphs below.

To use the hammock as an emergency heat reflector, just put it under the hammock and tie the two corners at each end up over the ridge line with a small reef knot. One of the guys at EcoChallenge Borneo showed me this trick and the space blanket fit like a diaper - you won't believe how well it works!

Hammock Pads
The next step in the search for the perfect pad was for a lightweight radiant reflector with attached insulation to prevent condensation build-up inside the hammock. We are also looking for a pad that does not interfere with the comfort of the hammock, does not pop out from under you in the middle of the night and provides comfort, efficiency, light weight and low cost.

Hammocks need a different kind of pad than a tent. Pads for tents are usually 20”-24” wide and thick enough to provide softness against the hard ground. Pads for hammocks do not need to provide any softness because the hammock is softer and more comfortable than any pad.

A pad for a hammock should be wider than a pad for a tent because a hammock conforms to the shape of your anatomy and the pad needs to insulate more of your body area than a tent pad. Ideally, the hammock pad would be as thin as possible so as to not interfere with the comfort of the hammock and provide enough insulation for the seasonal conditions. Thick foam or inflatable tent pads are designed to lay on a relatively flat surface. When used in a hammock, they are bent into compound curves which act like a loaded spring causing the pad to pop out from underneath you when given the first opportunity. This is most inconvenient when you wake up at 3 AM with a cold shoulder or hip and realize that the pad is sideways and that you will have to unzip your sleeping bag and sit up – losing valuable body heat – find the pad and wrestle it back under you. Then you have to zip up the bag and try to get warm again and back to sleep.

Auto windshield heat reflector pad

There are several types of auto windshield reflector pads. Some are folded cardboard with foil on one or both sides, some are a double layer of bubble wrap with a layer of aluminum foil laminated to each side and my favorite has 1/8” polyethylene foam with a piece of space blanket laminated to one side only.They come in all different sizes depending on the size of vehicle windshield. They will roll up to almost 2” in diameter and are around 4.5 oz. One nifty trick is to put this pad inside your sleeping bag so that it will stay aligned to your sleeping bag. If it does need a little adjustment, it is inside the bag and you can adjust it without unzipping your bag, losing body heat or waking up too much.

Tom’s experiment with Reflectix, windshield reflector pad, and fleece

I spent a couple of nights in the bush in September 2001 to experiment with reflector pads. Temperatures were in the mid 40s F (7ºC). None of this was very scientific, but the results were impressive. I used a 40" wide x 60" long piece of REFLECTIX tapered at the foot to 18" wide, a double layer of bubble wrap with aluminum foil laminated to both sides available (in different widths) from Home Depot, and an AUTO WINDSHIELD REFLECTOR PAD – 1/8' of polyethylene foam laminated to space blanket material. Comes in different sizes depending on the size of your windshield/body. I’ve heard that Wal-Mart has the biggest ones made for big trucks.

I sewed a piece of heavy fleece to the reflective side of the windshield pad but wearing a fleece suit would be as good or better. The fleece is important because it is fairly uncompressible and contains tiny air spaces necessary for radiant heat to pass through before it is reflected by the pad back to your body. Heat intensifies and, to me, felt like I was laying on some kind of solar cooker turned down to "warm". If your body is directly on the pad without the air spaces, you get the insulation benefits, but not the radiant benefits.

It was so comfortable that I did not need to be inside my bag so I just lay it over me like a quilt. Quilts seem to work well because they usually don't fall off because of the shape of the hammock. This was the most comfortable cool night I can remember.

Conclusion: Reflectix is an insulation manufactured mostly for the construction industry. It is used as a radiant insulating barrier in walls and wrapped around hot water heaters for additional insulation and also recommended as insulation for camping tent floors and insulation for hot and cold food containers. It is constructed of a double layer of bubble wrap with a layer of aluminum foil laminated to each side. It is around 5/16” to 3/8” thick and weighs about the same as foam pads of the same thickness.

The reflectix has several drawbacks. The raw aluminum will tarnish after a while, reducing it's efficiency. It is bulky and not as efficient as as the same thickness of foam and radiant reflector combinations. It's biggest problem is the heavy aluminum foil which is laminated to both sides. While it does reflect radiant body heat quite well, it also acts as a heat sink and the aluminum foil will suck heat out from under you wherever the aluminum foil is exposed to the cold air.

The windshield reflector pad is a much better solution to the problem. The closed cell foam is a better insulator than the bubble wrap and less bulky. The thin micro coating of aluminum reflective material is protected under a plastic coating, eliminating any tarnishing or any tendency to suck away body heat like the Reflectix did.

The dead air space between you and the reflector is an essential factor in the formula for radiant effficiency. If you sleep inside of your sleeping bag, the compressed sleeping bag insulation under you should have enough dead air space to allow the radiant pad to operate effectivelly. If you sleep directly on top of the radiant pad with your sleeping bag fully opened and laid over you like a big quilt, fleece material is probably the best way to get that dead air space between you and the reflector pad. For winter use, the fleece pants and fleece top make more sense since they are usable both day and night. Of course, fleece booties and fleece cap would really top it off. When wearing fleece clothing, you slip around quite nicely on the pad.

A windshield reflector pad facing up on top of a 3/8 inch thick urethane foam pad should take you down to around freezing. Ultralite backpackers will cut the full size 3/8 foam pad down to 36 inches long and keep the full length reflector because there is less weight and pressure on the pads under their legs. Total weight of this set-up is about 11 oz.

So far, this is the extent of our search for the perfect lightweight radiant reflector pad. The automobile windshield reflector pad offers attached insulation to prevent condensation build-up inside the hammock. It is flexible enough and does not interfere with the comfort of the hammock, nor does it pop out from under you in the middle of the night. Used in combination with additional foam pads of less than 3/8" provides comfort, efficiency, light weight and low cost.

Feedback: Gear Report from Rob - the long winded.  (I call him “toasty” now)
Hennessey Hammock (original) - The love fest continues. Someday I might upgrade to the ultralight to save a pound; otherwise the perfect shelter. WM Aspen bag, Jagbag liner. Reflector: Recently Tom Hennessey has been discussing strategies for staying warm in the HH. One item he mentioned was a windshield reflector with fleece sewn on one side. The fleece provides a non compressible barrier, creating the airspace needed for the reflector to work. Not being the sewing type, I hot glued fleece to a truck windshield reflector. On the first night, I had some trouble getting into my silk liner while staying on top of the reflector. The second night, I skipped the liner and slept directly on the fleece. Both nights I piled the unzipped sleeping bag around me like a quilt. Toasty the whole time. Rob

Feedback: Better than any tent...
I have good news for any Hennessy users who are contemplating using their hammock in cold (well, cold for me) weather. I went with my sons' Boy Scout Troop on a hike/campout in the Jefferson Wilderness in Oregon. Temperature Sat, night dropped to 20ºF. I am ecstatic to report that I slept better in my HH Expedition than I have in any of my tents, at any temperature. Hated to have to get up Sun. morning, I was so comfy.