ProView – Therm-a-rest Parsec 20 Sleeping Bag

“Thermarest? Don’t they just make sleeping pads? How would they know anything about a good sleeping bag?”

Those were my thoughts when I first heard that Thermarest had released a newly-designed “Fast and Light” line of human warmth burritos (sleeping bags as some may call them). I was filled with skepticism that Thermarest could match some of the titans of the bag industry. However, after several months of good use in late fall and winter conditions, my skepticism has been smashed down like a good boot pack. Although there is room for improvement in Thermarest’s Parsec bag, I was happily surprised with the quality and performance of the wide-use bag.

Therm-a-rest Parsec 20 Sleeping Bag

Product Description: Engineered for your fast and light adventures, the Parsec delivers lightweight and packable warmth. Just like an alpinist precisely selects his rack or a skier carefully chooses her line, we took the time to dial in the small details that create comfort and security in the mountains. After you break camp, the mummy-style bag uses a compression sack to easily fit into your pack without weighing you down. Designed with high-quality materials and Therm-a-Rest performance features, the Parsec easily handles three-season bivys and long pushes into the backcountry. Bottom line, those that need their sleeping bag to go further choose the Parsec. Storage sack and compression stuff sack included.

Offer price: MSRP: $369.95 - $409.95

  • Comfort
  • Features
  • Style
  • Durability


Overall, I give the Parsec four starlit bivvies out of a possible five. It’s size and weight, durability, and warmth make it one of the most versatile sleeping bags I’ve used. The bag is just as useful in the back of a Sprinter van as it is on a springtime alpine bivy. Future iterations of the bag will benefit from a darker color scheme and a more durable and smoother zipper.



  • Size
  • Weight
  • Durability
  • Warmth


  • Zipper sticks
  • Color shows dirt easily

Thermarest has called it “perhaps their most effective and well-rounded sleep system to date”, and I would have to agree. It’s sort of the jack-of-all-trades of sleeping bags. I think it would be insufficient for more committed alpine adventures, and it’s probably a bit much for casual summer outings. But it performs incredibly well in all other situations, and really is the most versatile bag I’ve owned yet.


Being a bit more grounded to the Midwest than usual due to medical school, I knew I wanted a bag that had versatility and warmth but wasn’t completely useless outside of winter or mountain environments (like my Mountain Hardwear 0 Degree Bag). I took the Parsec on several backpacking and climbing trips in the Midwest, using it in my car and tent as well as doing some backcountry bivvies. The bag’s 20-degree rating was comfortable across a wide temperature range and I found myself just as comfortable during 50 degree nights as I did in fifteen degree nights – depending on how I layered my sleepwear. Temperatures in the midwest can swing wildly during the night, and with previous sleeping bags I’ve found myself either terribly cold in the middle of the night, or far too hot in the morning hours. The Parsec managed these temperature swings surprisingly well, and I found that the dual zipper on the bag was perfect for opening a small window to allow some ventilation on warmer nights.

Also, I can’t fail to mention the warmth of the foot box. I often find that the foot box is a neglected area of many sleeping bags. Usually, it is too constrictive and lacks the same concentration of insulation compared to the rest of the bag. In the Parsec, my toes are as warm and happy as a baby joey in a kangaroo’s pouch. There is enough room to move my feet around but not so much that I feel I need to stuff other clothes there for insulation as I do in my other bags. The fit of the foot box (and the whole bag, honestly) – is one of the better combinations of comfort and warmth that I’ve experienced.

Size and Weight

By far my favorite aspect of this sleeping bag is its weight. Down will always have a weight advantage over its more dense, synthetic cousins, but it’s rare that I find any sleeping bag that doesn’t make me feel like I’m weight training when carrying my backpack. The Parsec achieved that and more. When I used the included compression sack, the bag shrank to the size of about two Nalgene bottles. I found that using a third-party stuff sack, like a Sea-to-Summit compression sack, can compress the bag even further. Usually, a sleeping bag takes up the entirety of the bottom of my pack, but I found with the compressed Parsec, I could slide my sleeping pad in next to it, and save some serious room for extra socks, trail mix, and a few beers.

The actual weight of the bag officially clocks in at two pounds, which is roughly the weight of one full Nalgene. When I held both the compressed bag and a full Nalgene in my hands, I honestly think the bag weighed less. For the first time in a while, my sleeping bag was not one of the heavier items in my pack.


The exterior of the bag is a very slick and seemingly thin synthetic layer, and I was immediately concerned about tears and holes if I used the bag on some rocky bivvies. Several times I would hear the bag run across a rock or a tree branch and think that I had just sliced it open, but every time I was relieved and impressed to find the bag unscathed. The material is more durable than it seems, I promise. The zipper seems to be holding up well, which is a contrast to my other sleeping bags where the zipper stitches seemed to be fraying and crumbling after only a few uses. My only beef with the zipper on this bag is that it CONSTANTLY gets caught on the surround sleeping bag material. Almost every time I zip up the bag, I have to un-jam the zipper. This is not a dealbreaker by any means, but I’m worried that this will eventually lead to tearing and loss of down. it seems like some simple design changes in the next iteration of this bag could easily solve this problem, such as a wider stitching base around the zipper, or the inclusion a longer leash on the zipper.


Another slight complaint is how easily the bag gets dirty. Although the “White Heat” color scheme definitely looks sleek, it’s already starting to brown and show aesthetic wear after just a few months of use.


Against my better judgment, I decided to bivy one evening in the Red River Gorge. Even in fall and early winter, the Midwest is infamous for its humidity and condensation. Well, I woke up at 5 am to find the Parsec bag completely saturated in dew. But, I quickly realized that I didn’t feel the same chill that I have in the past when my synthetic bags have suffered the same fate. The hydrophobic coating on the 800 fill Nik-wax down works. Period. The warmth inside my bag was still considerable, and I was able to sleep for another hour or so until sunrise without much discomfort.

What was more impressive than the bag’s ability to retain heat was it’s drying time. I hung the bag up on a clothesline during breakfast, and the bag was completely dry by the early afternoon. For a down bag, that’s simply incredible.

Overall, I give the Parsec four starlit bivvies out of a possible five. It’s size and weight, durability, and warmth make it one of the most versatile sleeping bags I’ve used. The bag is just as useful in the back of a Sprinter van as it is on a springtime alpine bivy. Future iterations of the bag will benefit from a darker color scheme and a more durable and smoother zipper.

This bag was my first foray into Hydrophobic down, and after being a strictly synthetic bag user for years, this bag has fully converted me to the church of waterproof feathers.

I have several trips to the mountains planned this spring, and from what I’ve experienced thus far, I feel confident that the Parsec can match my wildest alpine dreams.

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Sean has worked as a climbing guide and outdoor educator for the past four years and is also youth climbing coach at Hoosier Heights Indianapolis, as well as a Search and Rescue Technician. He spends most of his time in the Midwest, but has climbed in Mexico, Chile, Canada, Spain, and all over the United States. When not coaching or climbing, Sean is probably buried in his textbooks as he moves through medical school.

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