Sea to Summit Amplitude Double Sleeping Bag
This sleeping bag is an absolute must for all the couple campers out there who love the extreme conditions, but love spooning even more.
Size & Weight
Able to split up packed weight
Converts to quilt
Three zips for multiple air flow adjustments
Comfortable to -8C
Vertical chest baffles with side block baffles for extra warmth on sides
Great features like internal zip pocket & mat straps
On the heavier side at 2090g
Pricey at $800-$900

Not to give too much away, but this review quickly turned into a love letter to the double sleeping bag.

Kate Donald took a Sea to Summit Amplitude double sleeping bag for a spin in the Snowy Mountains this season and here’s what she found.


When my boyfriend and I go snow camping, there’s not much we disagree on. We share the weight of the gear, we make trip decisions together, hey, I even share my snacks with him. 

The harmony stays right up until bedtime. 

Snug as bug, Josh will fall asleep in seconds, nestled in his cocoon of warmth; I swear he could survive the winter with just a summer sleeping bag. Bitterly, I glare at him every time I stir through the night, adjusting my nalgene hot water bottle, to warm up whichever body part is coldest. 

I know I won’t be freezing to death anytime soon, all my sleeping gear is winter rated, but nothing could keep the chill out of my body, until now. 

Allow me to introduce the Amplitude AmIII Double Sleeping Bag from Sea to Summit. 



It’s a game changer for all couples or even cold sleepers willing to share a sleeping bag with friends.

And I know I’m calling it before the year is done, but this sleeping bag is my favourite outdoor purchase of 2021 – and I’ve been doing a lot of online shopping during lockdown.


Let’s start with the size; will you fit in this bag?

Josh and I are relatively tall people; we both own the extra-long sized sleeping bag and mat for our respective genders.

The recommended max user height is 183cm, but Josh is actually 185cm and it was the perfect length for both of us.

The hood fit over both of our heads, with our feet only just touching the bottom of the bag. As for the width, we found we both had plenty of space. A contoured rectangular shape, the internal girth measures 326cm across the chest, tapering to 319cm at the hip, and 282cm at the foot.

When we lay shoulder to shoulder, there was enough room on either side of us to not feel restricted as we tossed and turned during the night.

The extra room on either side of us also meant we could get in and out of the bag much easier, without unzipping or even disturbing our sleeping partner.

Insulation – Baffled By Baffles

With all that extra room, I was a little worried about cold air seeping in, but Sea to Summit have thought of everything. 

There are vertical baffles over the chest with block baffles on either side, to keep the warmth on top by stopping down migration occurring.

If you’re baffled by that sentence, ‘baffles’ are what we call the chambers stitched into the design of any sleeping bag or down jacket that compartmentalise the filling and stop it from moving around…

Basically, the baffles here are all extremely well placed and we never felt like a section was missing insulation.

These side block baffles also add extra insulation on the outer edges to trap the warmth in. The sleeping bag has a fill ratio of 60:40, meaning 60% of the fill is on top, and 40% on the bottom. Loft typically compresses with your body weight as you sleep overnight, so the less fill on the bottom means no down is wasted.



So how warm is it really? 

The bag is winter rated, with R.D.S certified 750+ loft down fill, the comfort rating is a cool -8˚C and a lower limit of -15˚C. When we tested it during our snow camping mission it was -4˚C and we stayed toasty warm. 

A snap lock button in the middle of the hood, means you lock in warmth by pulling the separate draw cords to close up your side of the hood. As temperatures warm up in the shoulder seasons, open the hood clasp and draw cords to allow air flow through the bag. 

As an added bonus, you can stop your phone battery from dying fast in the cold by keeping it warm too and storing it in the sleeping bag’s internal zip pocket!


Prepare yourself, there are a lot of zippers. The bag has zip’s down both sides, so that each person can open their side of the bag.

There is also a long zip across the bottom of the bag, this means you can unzip and poke your feet out on hot nights. With so many zips, and all of them opening up from either side, you can pretty much tailor it to however you sleep; leg out, foot out, you can even top and tail if you want.

With all these zips, you can unzip the top and bottom, separating them completely, and use only the top half in summer as a quilt.

The zips also overlap to make sure there is nowhere for the heat to escape. The down side; if you do unzip everything, it is a little bit fiddly to do them all back up due to these overlaps.


This may be the dealbreaker for some; weighing in at a whopping 2090g, the bag does not pack down very small when packed as a whole in the supplied compression bag. 

Sure, you can share the load with your friend, one carrying the tent whilst the other carries the sleeping bag, but we have an even better solution for you. 

We bought two Sea to Summit Compression Dry Sacks (a size S and XS), so we could split the sleeping bag and carry ‘equal’ weight. It wasn’t until we got to camp that Josh realised, they were in fact not equal, and he had been carrying the heavier of the two sleeping bags. The 60/40 fill ratio means the bottom is slightly smaller and lighter than the top; the weakest member of the team can carry this one. 


Added Bonus: Mat Straps

Before we got this sleeping bag, we used to use the Sea to Summit Mat Coupling Loops to keep our mats from sliding apart. The Amplitude Double bag has these loops already attached to the base of the sleeping bag. 

Not only does it stop the mats from sliding apart, and risking someone falling through to the cold ground, but they also keep the sleeping bag from moving about on the mats. 

The loops can be used for either two separate mats, or if you already own a double mat, they can be adjusted to loop around an entire double mat as well.

The Alternative – Zip Coupling Sleeping Bags?

Sea to Summit do make a few bags that perform ‘zip coupling’. This means the men’s and women’s bags are compatible to zip together into a double sleeping bag. 

The downside is these zips are only 165cm, so you have a separate footbox, meaning no footsies during the night. 

You also would have a zip in-between you both at the front and back, rather than the side zips seen on the Amplitude Double Sleeping bag. 

For those who enjoy spooning, that may get uncomfortable having a zip right underneath your back. Although the benefit of having your own sleeping bag on solo trips may be worth the sacrifice for some. 

The Amplitude Double Sleeping bag comes with a zip up storage bag, compression sack, mat loops and the best double sleeping bag you will ever use. 

It is the most versatile sleeping bag I have ever used; warm and cosy in winter, or a light and breezy quilt in summer.