Therm-a-Rest Parsec 0 Sleeping Bag Review

Backpacking season doesn’t have to end as the first snowfall hits the ground. Whether you’re looking to head out for a few days of snowy hiking, cross country skiing, snowshoeing, or ski touring, having a sleeping bag that keeps you warm and dry is key in ensuring you have a safe and enjoyable trip.

The Therm-a-Rest Parsec 0 is the go-to sleeping bag for winter adventurers. It checks all the boxes, with highly compressible 800-fill Nikwax Hydrophobic Down that absorbs 90% less water and dries 3x faster than it’s untreated counterpart, SynergyLink Connectors sleeping pad straps, and a down-lined Toe-asis foot pocket that keeps your feet cozy all night long.

Therm-a-Rest Parsec 0 At-A-Glance

  • MSRP: $529 (regular length)
  • Weight: 2lb 6oz (regular length)
  • Material: Hydrophobic down certified to the Responsible Down Standard + 20-denier recycled nylon shell
  • Tested Lower Limit: 0°F / -18°C
  • Tested Comfort Rating: 14°F / -10°C
  • Gender: Unisex
  • Fill Power: 800-fill-power Nikwax Hydrophobic Down

therm-a-rest parsec

Intended Use

The Parsec is designed for winter backpacking trips during the coldest weather. With the bag featuring hydrophobic down, the Parsec does extremely well in wet, snowy conditions.

Circumstances of Review

The Parsec was tested and reviewed on winter backpacking and camping trips throughout Western Colorado and Eastern Utah. Nighttime temperatures ranged from 0°F (with negative degree wind chills), up to 20°F. The reviewer tested a regular length bag and is a 5’2 female, however, she likely could have gotten away with the “short” length.

Therm-a-Rest Parsec 0 Features

  • Recycled liner and shell
  • 800-fill Nikwax Hydrophobic Down
  • Toe-asis™ Foot Warmer Pocket
  • External zip pocket
  • Heat-trapping draft collars
  • Draft zipper
  • SynergyLink™ Sleeping Pad Connectors

Draft Zipper

Choosing a Sleeping Bag

Although sleeping bags can come with an endless array of bells and whistles, arguably the most important feature to consider when choosing a bag is the temperature rating. This task has a little more to it though than just paying attention to the name of the bag.

How Temperature Ratings Are Determined: Sleeping bag temperature ratings are tested using an industry standard test to ensure ratings are consistent across brands and models. Most sleeping bag manufacturers send their sleeping bags out to an independent test lab that uses the EN (European Norm) or ISO (International Standards Organization) testing method to determine both comfort limits and lower limits across sleeping bags. After all testing is completed, the bag is assigned two different rating, the Comfort Rating and Lower Limit Rating

  • Tested Comfort Temperature: The tested comfort rating calls out the temperature at which a hiker who sleeps on the cold side would feel comfortable in the bag.
  • Tested Lower Limit: The Lower Limit is the temperature at which a warm sleeper will still feel comfortable in the bag. This number is almost always lower than the comfort rating.

It’s important to note that men’s and women’s bags are rated differently. Since a woman’s body naturally runs colder, sleeping bags designed for women will always use the comfort temperature rating in the product name. On the other hand, men tend to sleep warm, and sleeping bags designed for men will always use the lower limit in the product name. Unisex sleeping bags can vary in how they’re named, but in the case of the Parsec the bag uses the men’s naming convention and is marketed under its lower limit.

Temperature Ratings Are Estimates: Lab testing is designed to give as accurate of an estimate as possible for the average user, however since each person’s body is different, their comfort level in each bag will vary.  During lab testing, the sleeping bag is layed on top of a sleeping pad, and a test dummy is dressed in base layers inside the bag. While this method ensures all bags are tested the exact same way, it can not be accurate for every usage situation (such as differences in sleeping pads, gear, clothes, body types, health, etc). With all this being said, use sleeping bag temperature estimates as a tool to give you a close estimate on how the bag will perform, but expect to not treat these numbers as gospel and for there to be slight differences in how a bag performs in the field.

SynergyLink™ Sleeping Pad Connectors

Therm-a-Rest Parsec 0 Pros

Insane Warmth: Being a hiker who is quite literally always cold, I was excited – but not optimistic – about giving this bag a try. I was sure all the features would be killer, and the quality would be amazing, but I had serious doubts about any sleeping bag keeping me comfortably warm in the winter months. I’m pleasantly surprised to report that I woke up after a 0-degree night (with negative-degree wind chills) and had warmly slept straight through the night. Full disclosure, I did utilize a 15-degree sleeping bag liner in addition to the bag on this occasion, but nonetheless, I was blown away by the warmth of this bag. There was not a single night that I used this bag where I woke up cold, and I am ecstatic at how comfortable it kept me throughout the test period.

There are a few factors that help the bag keep you cozy all night long including the 800-fill down and a game-changing, heat-trapping draft color known as the Toe-asis™ Foot Warmer Pocket (which is a baffled pocket of insulation that helps warm cold feet inside the ergonomic footbox). Additionally, the bag utilizes heat-mapped zone insulation which maximizes warmth by utilizing insulation placed intentionally in areas where hikers frequently need extra warmth, while reducing insulation where it’s not as necessary. This not only helps keep your body warm in key places but dramatically brings down the weight of the bag, while also allowing it to be packed smaller in a stuff sack.

Keep Gadgets Warm: Being a commercial photographer by trade, keeping my camera batteries warm to prolong battery life is always a priority for me on backcountry trips. The external zip pocket kept my batteries and phone warm through multiple nights with single-digit temps, and I was able to wake up and shoot sunrise without skipping a beat – or missing my alarm due to a dead phone.

A Sleeping Pad’s Perfect Companion: Experienced backpackers know that in addition to a top-notch sleeping bag, a properly used sleeping pad is one of the best ways to stay warm throughout the night. The Parsec features two SynergyLink™ Connector straps which prevent your sleeping bag from sliding out as you sleep. This ensures you are able to take advantage of the added warmth your sleeping pad provides while staying cozy and tucked in, even if you toss and turn. If you’re wanting to keep things as light as possible, the straps are easily removable.

Therm-a-Rest Parsec 0

Heat-Trapping Draft Collars + External Zip Pocket

Therm-a-Rest Parsec 0 Cons

Could It Be The Perfect Bag? I’ve been racking my brain to find a con of this bag, and I have yet to find one. I am seriously blown away by how warm and comfortable it kept me, without making me feel confined or claustrophobic. One thing to note is that although I have used this bag on multiple trips totaling about nine freezing cold nights, long-term durability of the bag is yet to be determined. All signs point to this not being an issue, but I do not have first-hand experience aside from my nights spent in the bag.

For those new to winter camping, it’s worth noting that although this bag may seem heavy compared to summer models, the 2lb 6oz weight is extremely light for a 0°F bag. Winter bags also tend to not pack up as small, so do not let these two specs deter you from this killer sleeping bag.

Overall Value

I can’t say enough good things about this bag. Between keeping my frequently cold self warm on some of my coldest trips of the year, to the added touches and features that went into the design of the bag, I am blown away by how practical it is for cold weather adventurers. The bag truly opens up so many doors by keeping hikers warm throughout the night, which translates into a better night of sleep, and more miles the next day. I am already planning cold-weather trips for next winter, and you bet this bag is the first thing I jotted down on my packing list. Although a $529 price tag is no small purchase, the bag is pretty affordable compared to similar models shown below. If you are planning on doing frequent winter trips – whether that be backpacking, car camping, or anything in between – this bag is absolutely worth the investment and will pay for itself in how much more you can enjoy each experience by staying warm and well-rested.

Shop the Therm-a-Rest Parsec

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therm-a-rest parsec

*The Therm-a-Rest Parsec 0 was donated for the purpose of review.

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