Ask ten hammock campers why their first cold night was miserable, and nine of them will tell the same story: they had a warm sleeping bag, they had a good hammock, and they still froze from underneath. It's so common it has a name — Cold Butt Syndrome. The fix comes down to one decision that trips up almost every new hammock camper: sleeping pad or underquilt? Here's how the two actually compare, and how to pick the one that fits the way you camp.
Why your sleeping bag quits underneath you
Down and synthetic insulation only work when they're lofted — all those fibers trapping still air is what keeps you warm. The moment you lie on top of insulation, your body weight crushes it flat. In a hammock, your entire backside is pressing the underside of your bag or quilt against the fabric, squeezing out every bit of loft exactly where you need it most. Cold air moving under the hammock then pulls heat straight out of your back, hips, and shoulders.
On the ground you don't notice the crushed insulation, because you're lying on a sleeping pad — the pad, not the flattened part of your bag, is doing the bottom insulating. (The ground itself draws heat out of you quickly, which is exactly why ground campers carry a pad in the first place.) In a hammock you have no pad by default, and cold air is moving on every side. Either way, the job is the same: put an uncompressed layer of insulation between you and the cold below. That's why bottom insulation isn't optional in a hammock — it's the whole game. (We go deeper on why in Hammock Underquilt: Do You Need One?.)
The sleeping pad approach
A closed-cell foam or inflatable pad slides inside the hammock between you and the fabric, so you're lying on the insulation instead of compressing your quilt. It's the cheapest way to get warm in a hammock, and if you already own a pad for ground camping, it costs you nothing to try.
The catch is comfort. Hammocks curve, and flat pads don't — so pads slide out from under your shoulders, buckle at the edges, and leave your arms and hips cold when you shift in the night. Inflatable pads can feel crinkly and unstable in the gathered shape of a hammock, and a wide pad fights the hammock's natural lie. Most people who start on a pad tolerate it, they don't love it.
- Best for: budget setups, occasional hangers, and anyone who splits time between hammock and ground.
- Downsides: shifts around, cold shoulders and edges, flattens the hammock's comfortable diagonal lie.
The underquilt approach
An underquilt hangs outside and underneath the hammock, cradling it from below. Because nothing compresses it, the down stays fully lofted all night and wraps the curve of the hammock instead of fighting it. You get an unbroken layer of insulation from shoulders to knees with nothing inside the hammock to slide around or poke you. You lie directly on the hammock fabric — the way a hammock is meant to feel — and the warmth is just there.
This is the setup serious hammock campers land on, and it's what we've built at Jacks R Better since we introduced the first commercial hammock underquilts. It costs more than a foam pad and adds a dedicated piece to your kit, but for warmth and comfort in a hammock, nothing else is close.
- Best for: dedicated hammock campers, cold-weather trips, and anyone who wants to actually sleep well.
- Downsides: higher up-front cost; a dedicated underquilt is hammock-specific — though our multi-function quilts are built to double as ground insulation and a top quilt too, so you can have it both ways.
Underquilt vs. sleeping pad, head to head
| Sleeping pad | Underquilt | |
|---|---|---|
| Warmth in a hammock | Adequate; cold edges & shoulders | Excellent; full, even coverage |
| Comfort | Shifts, buckles, flattens the lie | Nothing inside the hammock; natural diagonal lie |
| Setup | Fussy to position, moves overnight | Clips on once, stays put |
| Weight | Light foam to heavier inflatables | Comparable; down is very light for its warmth |
| Cost | Lowest | Higher up front, lasts for years |
| Versatility | Doubles for ground use | Hammock-specific (unless you choose a multi-function quilt) |
When a pad still makes sense
We're not going to pretend a pad never has a place. If you're brand new and testing whether hammock camping is for you, a pad you already own is a fine way to get through a mild first night. If your trips regularly mix hammock and ground — some nights hung, some nights cowboy camping — a single good pad can cover both. And in genuinely warm summer conditions, the stakes are low enough that either works.
But the moment hammock camping becomes your default, or the temperature starts dropping into the 40s and below, the pad becomes the weak link. That's the point where almost everyone makes the switch.
The middle path: a multi-function quilt
If the one thing holding you back from an underquilt is that it "only" works under a hammock, look at a JRB multi-function quilt. These are designed to serve as a hammock underquilt, a hammock top quilt, and a ground quilt — one piece of down that covers every sleep system you own. It's the answer for the camper who refuses to choose between hammock and ground.
You can't overheat — so size up
Here's the piece of advice that saves the most cold nights: you cannot overheat from an underquilt. Because it hangs on the outside of the hammock, an underquilt only ever adds bottom insulation — if the night turns warm, you vent from the top, not the bottom. That's the opposite of a sleeping bag, where too much insulation means a sweaty, unzip-and-flail night.
What that means in practice: when you're between two temperature ratings, size up to the warmer one. A 20°F underquilt on a 40°F night just means a cozy night; a 40°F underquilt on a 30°F night means a cold one you can't fix from inside the hammock. Buy for the coldest night you realistically expect, and let the top quilt do your temperature regulation. (Full detail in our Hammock Underquilt Temperature Guide.)
Our recommendation
For dedicated hammock camping, an underquilt wins on every axis that matters once you've slept under one. If you camp mostly three-season, a 20°F underquilt is the versatile sweet spot; if you chase shoulder-season and winter, go 0°F and never think about it again. Trim, weight-focused backpackers can drop to a 3/4-length underquilt to shave ounces while still covering the core.
Every JRB underquilt is handmade in the USA with responsibly sourced down, built to loft hard and last for years of trail nights. Shop hammock underquilts → and put Cold Butt Syndrome behind you for good.