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How Do I Stay Warm in a Hammock?

Table of Contents
  1. Introduction
  2. Bulk Comparison
  3. Pads and their tricks
  4. Undercovers
  5. Overcovers
  6. Underquilts
  7. Spear PeaPod
  8. Pull-Up Bag
  9. Pockets Underneath
  10. Integrated Insulation
  11. Hammock Bivies and TravelPods
  12. Water Bottles
  13. Vapor Barriers
  14. Site Selection
  15. Natural Materials

Article: Four Season Hammock Camping

It Can Be Done
Photo by Doug Frick on BackpackingLight.com

Introduction.

Staying warm in a hammock presents a set of challenges not encountered by ground sleepers, and the methods aren't always intuitive. However, once a few basic principles are understood, a hammock camper can easily conquer these challenges and it's possible to sleep comfortably during all 4 seasons with little-to-no weight penalty over a ground setup.

Regarding hammock insulation, three issues must be addressed:

  1. Wind resistance - the wind will rob your heat by convection, so you must have some sort of windblock under the hammock
  2. Loft - the thickness of the insulation that traps your body heat
  3. Site selection - probably the most important, but it's not as sexy so I'll save it for last

Wind resistance is rather self-explanatory; it works like a windbreaker jacket. Protect yourself from the wind and you'll conserve heat.

Loft's function is not as intuitive. Here's how it works to keep a person warm in a sleeping bag:
Basically, wrapping yourself in insulation creates a tiny little climate around your body. The amount of warmth this "microclime" is able to hold is a function of a few factors, and one of the most important is the loft, or thickness, of the sleeping bag. When you climb inside and your body generates heat, the bag will trap tiny pockets of warm air inside the insulation. These pockets are what keep your body heat from escaping, and a bag with more loft (i.e. a thicker bag) will have more air pockets to protect you from the cold. Conversely, a thinner bag will provide less protection.

That's common sense...a thicker bag gives more protection than a thinner bag. But here's how this principle applies to hammock campers. When you sleep in a hammock, your body compresses the sleeping bag's insulation under you, so a bag that's normally 5" thick now provides about half an inch or so of insulation to your bottom side.

When you sleep on the ground, your pad provides a layer of insulation that prevents the cold ground from stealing your body heat. That's actually a pad's primary purpose...not to cushion you from the ground. In a hammock, on the other hand, you now have no insulation except a flat sleeping bag between you and the wind blowing under you that's robbing your heat. The first night I slept in my Hennessy, it was mid-30s and windy. I was in a -40° bag, believe it or not, and I was freezing on my butt and shoulders and sweating on my chest. So what's the answer? Find a way to better insulate underneath you! So how do you do that?

There really isn't a perfect or universally accepted method of insulating a hammock...everything is a tradeoff and what works for me may not work for you. However, hammock campers generally agree that underquilts are the most comfortable and expensive, while closed-cell pads are the cheapest and easiest, and still way more comfortable than sleeping on the ground.

The "best" way I've found so far is a DownHammock, but until I get it perfected I'll continue to use my JRB underquilt set or PeaPod. This page discusses many of the other common options.

Bulk Comparison.

Bulk Comparison
(Insulation Coverage)
(Measured Stuffed Size)
Notes: JRB has 2 oz overstuff. PeaPod is 900fp down with 2 oz overstuff and provides top and bottom insulation. CCF pad includes a 4" diameter circle in the middle to stuff gear into.

KAQ Potomac, JRB Nest, 1L Bottle
The KAQ isn't in a compression sack but I wouldn't feel comfortable compressing synthetic insulation much more than its stuff sack anyway. The JRB could probably compress a bit more, too.

Sleep with a pad in the hammock.

This is a very cheap and easy method of staying warm...buy a cheap closed-cell foam (CCF) pad from Walmart and put it inside the hammock. Just make sure it's wide enough. When you're sleeping on the ground, only a few parts of your body actually touch the pad, and the pad lays flat. In a hammock, the pad will wrap around you and you won't have any insulation on your shoulders. Many pads are only 20" wide, and this is too narrow for hammock camping. Walmart and Target sell 24" pads, like the Ozark Trail brand, that can work comfortably if you don't move around a lot. Better yet, get the 40"x60"x1/4" Oware pad from Oware USA and trim it to your specs.

A CCF pad (the dense rubbery kind) provides windblock because air cannot pass through it, and provides loft because its thickness does not compress when you lay on it. An open cell pad, like the egg crate mattress pads Walmart sells, will not hold warmth because it isn't windproof and will compress if you lay on it. Open cell pads can also soak up water like a sponge, which may be a disadvantage on the trail.

One benefit to carrying a CCF pad is that you always have it with you in case you want to sleep in a shelter. Also, if you get too cold you can always "go to ground" and abandon your hammock. With proper planning, this shouldn't happen.

I didn't like this option because a pad isn't as comfortable as sleeping directly on the hammock. Depending on the pad's thickness and amount of hammock sag, the pad can wrinkle and cause pressure points. More importantly, the closed-cell foam made me sweat so much that it soaked through the back of the sleeping bag. When I rolled over just a bit, the cold air hit my wet back and I was freezing, so I had to stay on my back until I was ready to get up and dry my bag. Others have complained about the difficulty of keeping the pad underneath them, especially when using a ThermaRest in a Hennessy.

I think the type of pad makes a HUGE difference, though. I've been using an Exped Downmat 7 with a JRB top quilt and I don't have the condensation issues that I had with the CCF pad, even when I was a bit overheated.

You can also use a few tricks to increase the coverage of a pad:

Sgt Rock's Wing Pad
Originally posted on Sgt Rock's page

Risk's Overlap Pad
Originally posted on Risk's page

The Speer Segmented Pad Extender
Photo originally on Ed's SPE page

My Homemade SPE
Pretty good coverage for a few added ounces

Rick Frost's Neat Frost Pad
Photo by Rick

Elastic Straps to Hold Side Pads on a Clark
Photo by Carol

Summary of Pads
Pros:
  • CCF pads are most durable and cheapest option
  • No worry about air gaps like with underquilt
  • Works when wet
  • Maintain go-to-ground capability with pad
  • SPE wing pads can be used as sit pads or frameless pack stiffener (or you can use extra clothing instead of CCF pads)
Cons:
  • CCF pads are least comfortable option (in my opinion)
    • Have to worry about staying on the pad when asleep
    • Condensation issues (CCF and inflatable pads are vapor barriers)
    • Pad can buckle, causing pressure points
  • Bulky to pack
A Few Examples: Cost (US) Weight (oz) Packed Bulk (in) Loft in Use (in)
Option #1: 2 x .25" CCF Pads (~45 F)
One full-length, one as wings or overlap
$25
12 oz
20" tall by 7" diameter
.5" for this weight
Notes: Rick's or Rock's pads, for example.
Option #2: CCF Pads w/ SPE (~20 F)
Full length .5" CCF pad
$12
15
20" tall by 7" diameter
.5" on center
Torso length .5" CCF pad
$12
7
20" tall by 4" diameter
.5" on center
SPE 2x2
$35
3.5
Tennis Ball
-
SPE Wings (cut from torso length pad)
-
8
5"x10"x4"
.5" in wings
Total:
$59
33.5
Bulky
1" on center
Notes: SPE makes it much easier to stay on pad and keep side insulation in position.
Option #3: Exped Downmat 7 w/ SPE (Possibly 0 F)
Exped Downmat 7
$120
31
7x7x7
2.8 on center
SPE 2x2
$35
3.5
Tennis Ball
-
SPE wing pads
$8
12
5x20x4
.5 on wings
Total:
$168
46.5
Not bad
Very Good
Notes:
  • Very comfortable
    • I haven't had any condensation issues like with CCF pads
    • Doesn’t buckle like CCF pads
  • Not bulky to pack like CCF pads
  • Inexpensive solution considering the possible temp range
  • Have to pump and deflate in camp
  • Possibly lose all insulation if a leak occurs that’s not field repairable

Windproof Undercover.

Overcovers.

Overcovers are a lot like undercovers, but they go on the top and trap heat inside the hammock. They work well to preserve heat in windy weather, but can get clammy in humid weather. In the pic of Sgt Rock's SuperShelter above, the under- and overcovers are all one piece...the new models have separate pieces, which allows moisture to vent out the sides. The HH version is ~3 oz of silnylon and has a big window at the top for ventilation.

Headchange4u made a DIY version from DWR...his doesn't have a window in the top, but DWR is breathable so it should be ok in most conditions. He basically made it the same shape as the HH bug net and put on attachments to hold it on the hammock.

DIY Overcover for Hennessy
Photo by Headchange4u

Underquilts.

Attach an "underquilt" to the bottom side of the hammock. If you're not lying on the quilt, it won't compress. Just make sure it's tight against the bottom of the hammock because any air space between the hammock and quilt will quickly get cold. This is the most comfortable way I've found on the market to stay warm in a hammock.

JRB Underquilt on a Hennessy
Pack Cover / Gear Hammock Attached

KAQ Potomac on a Hennessy
Photo from Whiteblaze

Mirage's Primaloft Underquilt...seals up like a PeaPod
Photo on Mirage's Page

Dennis Klinsky's Underquilt
Photo from Thru-hiker.com

Summary of Underquilts
Pros:
  • More comfortable than pads (in my opinion)
    • Breathable, no buckling pads, no worries about staying on a pad while asleep
  • Large coverage area
  • Leave it in snakeskins for quicker setup and teardown
  • Insulation adjustable by changing fit, “opening windows”, shifting down, etc.
Cons:
  • Price
  • Steeper learning curve
    • Precise fit required to minimize air gaps (more of a problem at colder temps)
  • Doesn't work as well as pads when wet
    • Down loses nearly all of its insulation ability, but synthetics retain most
    • Underquilts usually have DWR shells
  • No go-to-ground capability for cowboy camping, staying in shelters, safety for when it gets too cold, etc.
A Few Examples: Cost (US) Weight (oz) Packed Bulk (in) Loft in Use (in)
Option #1: JRB Nest (30-35 F)
JRB Nest Underquilt
$239
20.5
7"x7"x7"
2+"
JRB Suspension Set
-
1.5
-
-
Total:
$239
22
7"x7"x7"
2+" all over
Notes:
  • 78"x48" coverage (vs 30"x72" for pad with SPE 2x2
  • Multi-use as camp garment (leave worn insulation layer at home and save pack weight...saves me about 10 oz)
Option #2: Kickass Quilts (~30 F)
Kickass Quilt (Polarguard 3D)
$150
28
Bulkier than down
2"
Notes: 80" long, 48" at widest point (shaped to Hennessy Asym).

Ed Speer's PeaPod.

The PeaPod is like a down sleeping bag that completely surrounds the hammock and can get you to the 30s. You can add insulation inside the PeaPod, like his Top Blankets or dead leaves under the hammock, and use a top quilt inside the hammock, to increase the temperature range. Ed often sleeps with a pad inside his hammock, a PeaPod around it, and a Top Blanket used as a top quilt. The PeaPod won't work on a Hennessy.

MedicineMan wrote a pretty detailed PeaPod Review on Whiteblaze.net.

I've started my PeaPod Test page, which will eventually result in a full review when I get enough experience with it. I gained a lot of confidence in it at Winnemucca, though.

PeaPod in the Snow (Trip Report)

PeaPod at Winnemucca (Trip Report)

Summary of PeaPods
Pros:
  • Completely surrounds hammock
    • Top and bottom insulation (no top blanket needed for these temps)
    • Largest coverage area of any option
    • Air gaps not as important as with underquilt
  • More comfortable than pads (in my opinion)
    • Breathable, no buckling pads, no worries about staying on a pad while asleep
  • Leave it in (oversized homemade) snakeskins for quicker setup and teardown
  • Insulation adjustable by changing fit, opening top, shifting down, etc.
  • Multi-use as camp garment (leave worn insulation layer at home to save pack weight)
Cons:
  • Price
  • Body has to heat larger volume than with properly fit underquilt
  • Down loses nearly all insulation ability when wet (PeaPods have DWR shells)
  • No go-to-ground capability for cowboy camping, staying in shelters, safety for when it gets too cold, etc.
A Few Examples: Cost (US) Weight (oz) Packed Bulk (in) Loft in Use (in)
Option #1: 700fp PeaPod (45-75 F)
PeaPod 700fp down, no overstuff
$235
28
12"x17.5"
2.5"
Notes: 1.5" loft on bottom, 1" on top
Option #2: PeaPod All-The-Way (35 F)
PeaPod 900fp down, 2 oz overstuff
$365
31
12"x17.5"
3.9"
Notes: 2.2" loft on bottom, 1.7" on top. However, because of the large volume inside the PeaPod, I have to add a top quilt below about 50F. This brings the weight of the PeaPod to roughly the weight of the JRB 3-Season Set for the same temps.

Pull-Up Bag.

You can pull a sleeping bag all the way over a hammock so the hammock is actually inside the sleeping bag. I tried to zip my mummy bag around my hammock, but I couldn't get a good fit. Then I sewed a button-hole into the middle of the foot end, but I still couldn't get a good fit because the bag wasn't long enough. Another option is to cut a 6-7" hole in the foot end so the bag can slide up far enough to cover your shoulders (see pic). That's what Coy did in the picture below, and it kept him warm on our snowy night in the 30s at Hot Springs Campground.

You'll need to find a way to keep the head opening snug against the hammock so your warm air doesn't spill out; DebW put elastic around the neck so it snugs right up to the hammock with no adjustments. She also attached some material from the foot of the bag to the hammock supports to reduce lost heat (not shown in the pic below). Coy just stuffs a piece of clothing into the foot hole to act as a gasket.

DebW says it's not so tight as to restrict movement; she can still get on the proper diagonal and sleep on her side. Her bag still has its zipper so she can open it for ventilation. The bag might hang down quite a bit that way, though. She estimates her thin bag is good to ~50°F.

Coy's a big Alabama boy, and his bag restricts his movement a bit...he can't get diagonal, but he compensates by putting his heels on each side of the hammock to get the pressure off his knees and back. Must not be so bad if he still finds it more comfortable than sleeping on the ground.

Coy's sleeping bag over homemade hammock
Photo by Youngblood

DebW's Pull-Up Bag
Photo by DebW

Medicine Man's Western Mountaineering Ponderosa (15 F) Pulled Over a Crazy Crib Hammock
He only uses this below 20 F and reports no constriction
Photo by Medicine Man on Whiteblaze.net

Pockets Underneath.

The Clark Jungle Hammock has pockets on the bottom that you can stuff gear into for insulation, and some have integrated pad pockets to accomodate multiple sleeping pads. The pockets are on the right side in this picture.

Hikerhead's Clark Ultralight
Originally on Whiteblaze.net

Integrated Insulation.

Hammock Bivies and TravelPods.

My Hammock Sock adds more than 10° F of warmth, too. It keeps the wind from blowing across my underquilts much like the Taco, and if I use a ridgeline it keeps the wind from blowing across my toes. It gets humid inside if I breathe into it, but I haven't had any visible condensation yet. See HammockSock for instructions and my Foothills Trail Report for details about the tested temperature range. I even woke up in the snow at Hot Springs and didn't have any visible condensation.

HammockSock with Ridgeline

DebW's Hammock Bivy
Photo by DebW

Hot Water Bottles.

Water bottles can warm you up quickly if you become chilled at night. Just boil some water on your stove, pour it into a water bottle, slip the bottle into a sock (make sure it's sealed tight), and sleep with the water bottle against a major vein or artery. I like to put it against my groin (femoral artery) or in my armpits when I'm cold.

Collapsible water containers, like Platypus bladders or Nalgene soft-sided cantenes work great for this. My current favorite is a soft-sided 3L Nalgene cantene...I put in the hot water and lay it on my body (usually on my belly or femoral artery), and it shapes exactly to wherever it's laying. Then as it cools up I can use it as a pillow, too.

Cautions:

Vapor Barriers.

Vapor barriers are a somewhat controversial topic. Do some research if you're inclined to use this method. One good source is Stephenson's Warmlite page.

The closest I come to vapor barriers is sleeping in my rainsuit. I wear thin polyester long johns, then my rain suit (breathable, so not really a VB), then I put my fleece jacket on top. I think it helps a little but I haven't done any testing to confirm. One time I slept with my fleece inside my rain jacket, though, and the fleece was wet when I woke up, so it makes some difference.

Site Selection.

(Acknowledgements to Ed Speer's Hammock Camping book, among others)

Just like tenting, selecting the proper site may be the most important skill to staying warm (or cool) in a hammock.

When searching for a campsite, the hammock camper is free from the constraints of many tenters...no need for level ground, no worries about rocks or roots, no concern for drainage, etc. However, even in a good site the hammocker is more vulnerable to wind and temperature shifts than a ground sleeper. One of the most important factors in the suitability of a hammock site is how exposed it is to the wind. If warmth is the goal, search for sites with natural windblocks like dense vegetation, boulders or cliffs.

Camping on the leeward side (as opposed to the windward side) of ridges and hills can make a substantial difference. In the Southeastern U.S., the weather generally blows in from the West to the East, so in the winter I usually camp on the Eastern side of ridges. This also offers the advantage of morning sun to heat up the site before I get moving.

Additionally, sleeping at the top of a hill or ridge will expose you to the wind, but sleeping at the bottom will also put you in a cold zone. As warm air rises, cold air sinks to the lowest elevation, creating a "cold sink" as temperatures drop during the night. Search for sites midway up ridges and hills.

If a stream is running along the valley floor, the temperature could be 5-10° F colder than the temperature of a site with only thirty feet or so of elevation gain! Lakes can have the same effect, so look for sites not located near water, especially running water like streams and rivers.

Hammock orientation also plays a role. If the wind is coming from the West, orient the hammock North-South and pitch the tarp close to the ground on the windward side. This will add another layer of windblock to your hammock. If you would like to take advantage of the wind to cool you off, orient your feet into the wind and angle your tarp to deflect the wind onto your hammock.

When selecting a campsite to stay warm in the winter, look for sites that are: When selecting a site to stay cool in the summertime, look for sites that are:
  • Protected from the wind:
    • Near natural windblocks, like vegetation or boulders
    • Midway up a ridge or hill
    • On the leeward side
  • Away from water, especially streams and rivers
  • Oriented perpendicular to the wind (use tarp as windblock)

  • Exposed to the wind:
    • No natural windblocks
    • On top of a hill or ridge
    • On the windward side
  • In the bottom of a valley to be in the "cold sink"
  • Near running water
  • Oriented in-line with wind direction (use tarp to "catch" the wind)

Natural Materials.

In addition to picking a good site with natural windblocks, nature offers other ways to keep a hammock warm. Ed Speer writes in Hammock Camping that dry leaves can be used between the PeaPod and hammock to add more loft. While I don't like the idea of putting vegetation inside my insulation, it can certainly help in a pinch.

But Medicine Man came up with a pretty good solution that combines natural materials with site selection. He pitches his MacCat Deluxe all the way to the ground and hangs his hammock a few inches off the ground. Then he piled up some leaves and duff (which you can't see very well in the picture) so the hammock is actually laying inside the pile. The hammock still supports his body weight, but the leaves and duff prevent the wind from blowing under the hammock, which reduces convective heat loss. Great idea, MM! Just be sure to scatter your pile when you break camp so you Leave No Trace.

And NigelP took the below picture in France...it's almost a snow cave! Great idea, and it looks like it blocked quite a bit of wind.

Medicine Man's MacCat and Duff Pile
Photo from Whiteblaze

NigelP's Hammock Cave
Photo from Hammock Forums

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