Therm-a-rest Questar 0F/-18C Sleeping Bag | Review - Outdoors Magic

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Therm-a-rest Questar 0F/-18C Sleeping Bag | Review

Cosy, roomy and comfortable, this is a fully-featured and reasonably priced four-season sleeping bag that works well for winter wild camping adventures

Though still best known for its sleeping mats and pads, Therm-a-rest also makes some of the best sleeping bags in the business. We’ve previously tested (and been seriously impressed with) the brand’s Parsec series, a range of 800 fill power down bags that strike a great balance between weight, performance, comfort and affordability.

In contrast, the Questar 0 is a slightly lower spec sleeping bag than the Parsec 0. It’s still designed for four-season use, and maintains the focus on those four attributes listed above, though with a slight bias towards comfort and affordability. As such, it has a slightly roomier fit than the Parsec, ideal for those who like a little more wriggle room. It also uses a slightly lower grade of down fill than the Parsec (650FP rather than 800FP), which keeps the price down.

When it comes to performance, it has exactly the same EN temperature ratings as the Parsec 0, namely a comfort rating of -10° Celsius (14 degrees Fahrenheit) and a lower limit of -18° Celsius (0 degrees Fahrenheit). So, there’s no trade-off in performance there.

On the scales, the regular size weighs in at 1.21kg (there are also small and long versions of the bag). In comparison, the regular Parsec 0 weighs 1.09kg. So, the Questar is a little heavier, though not a lot. It also has a slightly larger packed size. But it is also more than £150 cheaper, representing a significant saving.


The shell fabric of this bag is 20-denier polyester finished with a durable water repellent (DWR) treatment, which does a decent job of keeping minor tent spillages and condensation out of the bag’s down fill. If you’re bivvying, it has no trouble repelling light frost or dew either.

The lining is also made from 20D polyester taffeta, which is soft and comfortable, even against the skin.

The bag is filled with 820g of 650 fill power duck down, certified by the Responsible Down Standard. The down is also treated with a Nikwax hydrophobic finish, a water-repellent coating that means it absorbs 90% less water and dries 3 times faster than untreated down. Nikwax’s testing has also shown that it maintains its loft 60 times longer than regular down. Like all Nikwax products, the DWR treatment is free from harmful PFCs.

This should help to guard against general dampness – though as with all down gear, it’s good practice to try and keep your down dry, as a soaking wet down bag makes for a cold and sleeples night. Still, it’s a useful additional measure of weather resistance that means you won’t be totally screwed if your sleeping bag gets a bit wet.

OM editor Will with the Questar on a campout in Scotland. Photos: Dave Macfarlane

Of course, 650 fill power down doesn’t loft as well as 800 fill down, giving it a lower warmth-to-weight ratio than the Parsec or rival 800FP bags. But there’s plenty of fill here to ensure ample warmth in sub-zero conditions, and the bag’s overall weight and packed size is competitive. It is by no means too big to be a viable choice for backpacking or wild camping. Sure, it’s not ultralight, but it’s still far more portable and packable than a synthetic alternative.


Here’s where the Questar 0 really shines. It’s fairly loaded with features. First is the overall cut, which Thermarest calls its ‘W.A.R.M. fit’ (‘With Additional Room for Multiple positions’). It’s basically a clever way to describe the relaxed mummy shape, meaning this bag allows for various natural sleep positions while maintaining thermal efficiency. It actually measures a generous 63 inches in circumference at the shoulders, so it’s a great bag for broader builds, as well as side and front sleepers.

Another clever innovation with an equally nifty name are the Synergylink connectors. These are removable elastic straps that connect the bag to a sleeping mat, ensuring you won’t roll off your mat onto the cold ground in the middle of the night. This also maximises the benefits of the bag’s zoned insulation, which places more down fill on top and the sides of the bag, and less underneath, where it would be compressed by your own bodyweight anyway.

Next, there’s a ‘Toe-asis’ foot pocket. This is an integrated footwarmer inside the bag that eliminates some of the dead space at the bottom of the bag to keep your feet warmer. It works really well – ideal for those with poor circulation.

Up top, there’s a cosy, snug-fitting hood with a drawcord closure, plus a padded neck baffle for improved thermal efficiency.

The two-way zipper has a smooth-running, (almost) snag-proof insert to stop it from getting stuck on the thin fabrics. It’s backed with a full-length insulated baffle, reducing cold spots. It is also positioned slightly higher on the side of the bag to ensure it’s easy to reach, even when the bag is connected to a sleeping mat.

Lastly, the bag features a small external zippered pocket, ideal for stashing tent essentials. It will also help to keep camera, phone or headtorch batteries warm, though not that the pocket itself is not insulated, so you might still be better off sticking them in the bag with you for ultimate peace of mind.

All in all, the Questar 0 packs an impressive number of features in a great value package. If you need an all-round winter bag for UK use that comes in at well under £400 (and considerably less if you shop around), it’s a top choice.

Tester’s Verdict

Dave Macfarlane, Adventure Photographer and Videographer

I can’t count the number of times I’ve slipped off an inflatable mat in the middle of the night to find myself laying face down on the groundsheet, the only time this doesn’t happen is if I’m bivvying but that’s more like being the meat in a sausage and a story for another time. Thermarest have developed their SynergyLink Connectors that are essentially sleeves to the rear of the bag that allow the mat to slide in and be connected to the sleeping bag. Genius. I love this and with ample shoulder room for all night wriggling this is my new go-to bag.

Thermarest Questar 0F/-18C Sleeping Ba

Selected for the Outdoor 100 Winter 23/24
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