Therm-a-Rest Parsec Series Sleeping Bags | Deep Dive - Outdoors Magic

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Therm-a-Rest Parsec Series Sleeping Bags | Deep Dive

Meet the Parsec series; Therm-a-Rest’s newly updated, improved and expanded range of premium down sleeping bags, designed for fast and light adventures.

In astronomy, a parsec is a unit of measurement used to express the distance between various celestial bodies or objects – like how far the planets are from the sun. Apparently, 1 parsec equates to about 3.26 light years. Which is a very long way away.

But no matter how far you are from home, Therm-a-Rest’s new Parsec sleeping bags are designed to deliver toasty warmth, all night long. And since it’s unlikely you’ll be going anywhere that compares with the intense cold of interstellar space (not much above absolute zero, which is -273.15° Celsius or -459.67° Fahrenheit, in case you were wondering), their premium 800 fill power down should be able to keep you perfectly cosy.

A Trio of Options

In fact, to increase the Parsec’s suitability for a wider range of temperatures and conditions, Therm-a-Rest have also added two more options to the line-up for 2022. Until now, the only bag in the Parsec series was the 20°F/-6°C model, with an EN comfort rating of 0°C (32F) and a lower limit of, you guessed it, -6°C (20°F). That’s the sort of temperature range that makes for a solid three-season sleeping bag, ideal for wild camping and backpacking adventures from late spring through to early autumn.

However, to cater for dedicated winter warriors, there’s also now a slightly bulkier and heavier but significantly warmer Parsec 0°F/-18°C, which is designed to remain comfortable even if you’re out in sub-zero temperatures that drop into double digits.

And for ‘fast and light’ backpacking trips in the warmer months, when either of the two other bags would be overkill, there’s a Parsec 32°F/0°C, intended for nights that could get a little chilly but won’t dip below zero.

Unlike a lot of rivals, all the bags are available in small, regular and long lengths too, ensuring a tailored fit whether you’re 5ft 6 or 6ft 5. In terms of weight and pack size, they’re also very competitive. The regular sizes tip the scales at 685g (32°F), 805g (20°F) and 1,090g (0°F) respectively, with the smallest option packing down to around the size of a 1-litre Nalgene bottle. Therm-a-Rest have also managed to shave a little weight off the new 20°F/-6°C model compared to the previous generation.

They’re all supplied with a compression stuff sack for efficient packing, plus a cloth storage bag that will allow the down fill to loft when not in use, prolonging the life of your sleeping bag.

Who is the Therm-a-Rest Parsec Sleeping Bag for?

With three different bags designed for use in the different seasons, and three different lengths available too, the Parsec range is undoubtedly versatile – it’s a cliché, but there really is something for everyone here.

Photos: Therm-a-rest

However, the emphasis of all three models is squarely on ‘fast and light’ adventurers. A number of design features ensure these bags are pretty much perfect for wild camping and backpacking, when you need to balance weight and warmth.


Firstly, there’s the fact that all the Parsec bags are stuffed with premium 800 fill power down, which offers excellent warmth-to-weight. Their boxed baffle construction also helps to eliminate cold spots – unlike stitch-through bags, they won’t leak precious heat at the seams.

The insulation itself is also strategically placed, or ‘zoned’, with 60% of the fill placed on top and 40% on the bottom. Putting more of that lofty down on top, where it won’t be compressed by your own bodyweight, further improves the bag’s warmth-to weight ratio, whilst allowing the sleeping mat underneath you to do its job of insulating you from the cold ground. The boffins at Therm-a-Rest worked out the optimum zoned fill weights following extensive testing in their on-site cold chamber in Seattle, ensuring the perfect balance of thermal efficiency and weight.

The fill itself is certified by the Responsible Down Standard, ensuring it is sourced from geese that have been treated humanely and not live-plucked.

The down clusters have also been treated with Nikwax’s eco-friendly hydrophobic chemistry to improve their resistance to moisture. This is traditionally the Achilles heel of down, since down tends to collapse when it gets saturated, losing its loft and robbing it of all that precious, air-trapping warmth. However, test results show that Nikwax hydrophobic down absorbs 90% less water, dries three times faster, and maintains its loft up to 60 times longer than untreated down. That should give backpackers and wild campers a lot more reassurance whether they’re out on damp, cold nights or warm, humid ones. No more drama if the head or foot end of your sleeping bag accidentally brushes against the inside of your tent, tarp or shelter.

A demonstration of just how small the Parsec 20F/-6C can pack down.

What’s more, as well as reducing the environmental footprint of the down fill, Therm-a-Rest have also focused on improving the sustainability of the fabrics used for the sleeping bag’s shell. They’re made from a 20-denier nylon, which is 100% recycled and certified by the Global Recycling Standard. This is a real step forward that deserves plaudits. Relatively few top-end sleeping bags incorporate recycled materials – which is a shame, especially when you think about the sheer volume of materials involved in making a sleeping bag compared to something like a rucksack or a waterproof jacket. It’s a topic we’ve addressed before in our piece on The Most Sustainable Sleeping Bags. So, it’s great to see Therm-a-Rest taking the industry forward in this regard. The bags are also free from PFOAs, the long chain (C8) perfluorinated compounds that are arguably the most harmful and environmentally persistent chemicals in the outdoor industry.


Unlike many rival brands, Therm-a-Rest’s extensive range of sleeping bags utilise three different fits, designed for different end uses. The Parsec series uses the brand’s performance fit, which occupies a versatile middle ground between their comfort focused W.A.R.M fit and their streamlined Ultralight fit.

The performance fit is a conventional mummy style, which maximises thermal efficiency and minimises pack size, but still provides enough width for a comfortable sleep. It isn’t quite as aggressively tapered as something like the ultralight Therm-a-Rest Hyperion, for example, giving you a little more wriggle room – which makes the Parsec better suited for side sleepers or toss-and-turners. In addition, the 0°F Parsec bag – designed for four-season use – is cut slightly roomier than the other bags in the series, allowing you to wear additional layers for extra warmth.


These bags are engineered with a host of practical features, making for fuss-free life outdoors. Take the zippers, for example – always the most frustrating part of getting in or out of a sleeping bag (especially at 3am, when it’s pitch black and you really, really need a wee).

Therm-a-rest have made snagged zippers a thing of the past. Photo: Michael Drummond

The Parsec series utilise YKK snag-free zips, which feature a special slider design that virtually eliminates the possibility of snagged fabric and stuck zippers. In fact, one of our regular kit testers here at OM, North Wales-based photographer Grant Hyatt, had a good go at trying to get the zip to snag when he nabbed this bag for an overnighter on this year’s Outdoor 100 gear testing trip. He failed, every time – just one reason why he was so impressed with the Parsec (read the full review here). It was no surprise that it waltzed straight into the final selection for the Outdoor 100 2022/23, our round-up of the season’s best gear of the year.

All the other features that you’d expect to find in a quality sleeping bag are present and correct. This includes a cinch hood, a draught tube at the collar and a padded baffle behind the main zipper. There’s also an ergonomically designed foot warmer pocket that the brand calls ‘Toa-asis’, specially shaped to keep feet cosy. There’s even a useful zipped external pocket to keep small essentials close at hand. In our experience, this is a great place to stash a phone, camera battery or power bank, keeping them warm to prevent power drain.

We also like the fact that the Parsec bags take something of a modular design approach too – by which we mean you can use them in conjunction with Therm-a-Rest’s sleeping mats, quilts and blankets to create a unified and cohesive sleep system. The bags feature removable Synergy Link connectors – updated to be lighter than before – which allow you to physically attach the bag to your sleeping mat. This is a clever idea that helps to prevent roll-off and heat loss. You’ll particularly appreciate it if you’ve ever slid off your mat during the night and then woken up shivering, curled up in a ball on the floor of a freezing cold tent.

Similar blanket attachment loops at the sides of the bag also allow you to couple the Parsec with a Therm-a-Rest quilt or tech blanket, effectively adding an extra top layer that won’t just slide straight off. This enables you to create your very own customised sleep system that boosts overall warmth – handy if night-time temperatures plunge lower than expected.


The Parsec bags really tick all the boxes for us in terms of a great all-round sleeping bag for weight-conscious camping and backpacking.

They’re light and packable, with great warmth for weight. That’s thanks to the premium 800FP down, which also features that Nikwax hydrophobic treatment for superior performance in damp conditions compared to untreated down. The nylon shell is soft but strong, whilst also being made from recycled fibres, which is a big tick for sustainability. So, both the fabric and fill are focused on delivering high-level performance but are also environmentally sound.

The three difference lengths and versatile Performance Fit also ensure these bags are comfortable yet thermally efficient too, whatever your size and shape. And then there’s the fact that they are well-made and cleverly engineered with a range of thoughtful, considered and practical features. They’ll work particularly well if you also own a Therm-a-Rest mat or quilt, thanks to that modular and integrated design.



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OM x Therm-a-rest
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