the Logo on the Thermnarest Questar -18 Sleeping Bag

Review: Thermarest Questar

Review: Thermarest Questar -18 Review

The Thermarest Questar is a comfortable, warm and easily compressed sleeping bag that ticks all the boxes for just about anything overnight backcountry tips can throw your way.  It contains 650 fill hydrophobic down, has a comfortable Mummy shape and rated to -18C. Add in the ability to attach it to both a sleeping pad or an accompanying down quilt and you’ve got the core of a very capable and comfortable backcountry sleeping system. 

We’ve spent more than 30 nights in the Thermarest Questar -18. Read on to see what we thought of it. 


  • Weight: 1.21 kg
  • Width: 31.5 in
  • Length: 80in
  • Shoulder girth: 160cm
  • Hip Girth: 155
  • Footbox Girth: 117cm
  • Fill weight: 1lbs 13oz / .82kg
  • Shell: 20d polyester w/ DWR
  • Lining: 20d Polyester Taffeta
  • Made in China

How Warm is the Thermarest Questar  -18?

This is a great general-purpose sleeping bag for the winter or anyone who’s a cold sleeper. And though its name is the Thermarest Questar -18 sleeping bag, it is important to note that -18 is the extreme limit rating. Its comfort rating is actually -10c. I haven’t had the chance to use this bag at quite that cold of a temperature yet but have no doubt it will be warm enough to handle it given how great it’s been when I’ve been out. And I wouldn’t want to use it on a warm summer night but if you are spending the summer high in the rocky mountains, it may not be a bad idea.

The Questar is filled with 650 fill Nikwax Hydrophobic down. This down, as the name implies, has been treated with Nikwax so it absorbs 90% less water and dries 3 times faster than untreated down. A really great feature as tents often get damp overnight with dew/moisture from breathing. To further the warmth of the Questar, it’s constructed using Zoned Insulation. Thermarest places more down filling where you will need it most and conversely, less where you need it… well, less. A very weight efficient way to squeeze a little extra performance out of a bag.

There is 820 grams of down fill in the Questar -18. All of that down is held in place by Box Baffles. Thermarest uses mesh walls between the chambers of down to maximize loft, minimize cold spots, and of course, stop the down from shifting around. For more info on Box Baffles head here:

Duck Down

Shows Thermarest Questar -18 details
The Thermarest Questar -18 fine details

The Thermarest Questar is filled with Responsible Down Standard Certified down. This is a Certification that ensures that the waterfowl in the down supply chain are treated humanely. 

Most people assume myself included, that anything that is made with down is being made with goose down. This is just no longer the case. The cost of goose down is quite high and so many manufacturers have switched to using duck down. From the research I have done, there is very little difference between duck down and goose down. I’ll quickly outline what they are here:

Loft: Only geese produce down that is of the very high loft: think 800 fill power. Durability: About the same. 

Warmth: 650 fill power is 650 fill whether it is duck or goose. 

Odor: This is where they often vary. The Thermarest Quesar -18 had no odor to it at all. I suspect this has as much to do with the cleaning as it does with the feathers being coated.

Anecdotally, I bought a duck down sleeping bag once before. Within an hour I had an asthma attack due to the down. I was apprehensive about the Thermarest Questar but had no problems at all. 

Thermarest Questar Features

Thermarest Questar Sleeping Pad attachment
The Thermarest Questar -18 Sleeping Pad attachments

The Thermarest Questar is packed with features. The first notable feature is the SynergyLink connectors. They wrap around your chosen sleeping pad keeping you from either rolling off your sleeping pad or rotating the bag as you roll around at night and potentially end up with the zipper top side or the whole bag flipped leaving the bottom, less insulated side, top-up.

This feature works quite well, though while using it on a wide Exped sleeping mat, the connectors were quite taught and I was worried about ripping the bag. With a normal-width sleeping mat, this would not be a problem. Though this is also removable, I could not actually remove it. The tolerances between the loops and the SynergyLink Connector were just too tight. Was this a genuine problem? No.

Thermarest Questar Sleeping Pad Attachment Clips

The Thermarest Questar also has a rather substantial draft collar and a full length zipper with a matching draft tube. There is a snag-free zipper that does its job well. 

Something that proved handy was the small external zip pocket. I put my phone in there most nights and then it does not drop to ambient temps and it does not have to jostle around in my bag to stay slightly warm.

It also comes with a compression sack and a storage sack. The compression sack is quite nice for a stock compression sack, though I didn’t use it. I prefer to stuff my sleeping bag loose in the bottom of my pack.

The sleeping bag also has a very generously sized hood. So big in fact I was able to put my Large size pillow inside of it to keep the pillow from moving around. Perfect. 


Thermarest Questar -18 Sleeping Bag ClosureThis is one exceptionally comfortable sleeping bag. Thermarest states it comes with a W.A.R.M. Fit. This acronym stands for With Additional Room for Multiple positions. What it means to you and me is that it has a generous cut, one designed to allow for rolling over and side sleeping. 

There are also quilt and blanket loops on the side of the sleeping bag. If a comfort rating of -10 on your sleeping bag isn’t quite enough and you happen to own a Thermarest Down Quilt, you can attach the two of them for an über warm pairing. I have yet to try this but I certainly will this winter. 

Inside the sleeping bag is one extra bonus, the Foot Warmer Pocket. This is a small extra compartment at the foot of the sleeping bag to help keep your toes toasty. I still like to add a hot Nalgene on the extra cold nights, though.  

The hood is large and easily accommodates an inflatable pillow. 

Thermarest Questar Sizing

Thermarest Questar -18 in tent

I have a size large. Thermarest suggests that a size large fits folks up to 183cm in height. I am 187cm and find it fits me just fine. Packed down in it’s included stuff sack the sleeping bag is not much bigger than a Nalgene bottle. 


The Questar -18 comes with two bags. One a compression sack and the other a cotton storage sack. Admittedly, I do not use the compression sack. While in the backcountry I put the sleeping bag inside my inflation bag. While at home I keep it stored inside the cotton bag. This allows the down to maintain loft and not be in a constant state of compression. That said, if you are compression bag user, this is a nice addition to the bag as many other brands force you to buy a compression sack. 

Summary of the Thermarest Questar

Pros: Great Quality at the price point, tons of features, part of a great sleeping system that can be expanded when needed.

Cons: Confusing Temperature Rating

Overall: The Thermarest Questar has proven to be a great sleeping bag in cool to cold weather and in the summer in the Alpine. It’s extremely comfortable and the price point, it will be hard to beat. Admittedly, you can get lighter sleeping bags for the same warmth, but to do this you’re going to be moving over to an 850 fill bag, likely filled with only goose down, have less room and pay a lot more. This isn’t a minimalist bag but rather a lightweight workhorse. The Thermarest Questar -18 is a good compromise of function and price and is a great addition to most hiking and backcountry overnight kits.

Black Sheep Adventure sports was provided with a free DB Hugger to test. This in no way affected our opinion and review of the jacket.

Looking for more Thermarest reviews? Hit this ling for the Parsec and Corus Sleeping System review: