Therm-a-Rest Parsec Sleeping Bag Review

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Therm-a-Rest Parsec

Springtime weather in the Rockies is unpredictable. One day it looks like summer is right around the corner and then the next day feels like mid winter. This variability makes choosing a sleeping bag challenging. This spring I am stepping up my sleeping bag game with the Therm-a-Rest Parsec Sleeping Bag. 

Storage Sack

Therm-a-Rest Parsec 0F compressed down

Since the early 1970’s Therm-a-Rest has been an innovator in the outdoor sleep industry. The company was founded on inflatable sleep pads but over the fifty years of business Therm-a-Rest expanded to sleeping bags, camp pillows and camp gear. This year Therm-a-Rest has expanded its popular Parsec Sleeping Bag line up to three different bags. The Parsec line now includes a 0℉, updated 20℉, and a 32℉ sleeping bag. For my first camping and backpacking trips this spring I am excited to try out the 0℉ Sleeping Bag to see how well it handles the varied weather conditions.  

About the the Therm-a-Rest Parsec 0℉ Sleeping Bag

The Therm-a-Rest Parsec 0℉ Sleeping Bag is the second warmest sleeping bag that Therm-a-Rest offers. This bag is specifically designed for cold winter conditions. The lower limit of this sleeping bag is 0℉ and the lower comfort limit is 14℉.  

Comfort Rating

This bag has an 800 Nikwax Down Fill. The 800 fill makes the bag highly compressible for the amount of down needed to achieve it’s 0℉ warmth. Nikwax Hydrophobic Down is pretty awesome. This down has been treated so that it absorbs 90% less water and dries 3 times faster than traditional down.  

The down fill has been strategically placed throughout the bag. Heat mapping technology was used to image the areas that require the most warmth. A system of baffles allows the bag to use less down to achieve the proper amount of warmth. Additionally, different areas of the bag contain varying distributions of down. Areas that require more warmth are loaded up. 60% of the fill is located on the top of the bag and 40% is located on the back of the bag where a sleeping pad would be underneath. Additional fill is also added to the toe box of the bag, which is an area where campers often get cold.  


Therm-a-Rest put a substantial amount of thought into the fabric design of the Parsec Sleeping bag. Concerned with the ecological footprint, there has been a large effort to incorporate recycled fabric into the sleeping bag. The nylon used in both the interior and exterior comes from 100% recycled material. Not only is it ecologically friendly but it is also chosen for softness and comfort. 

A special YKK zipper has been used where the sleeping bag opens up. This zipper is snag free. The idea behind this is so that the nylon exterior does not get zipped up into the bag. This is the cause of many tears in the exterior fabrics of sleeping bags. Additionally a small storage pocket has been added to the to the exterior of the bag.  

YKK Anti Snag Zipper

Therm-a-Rest Parsec 0F Storage Pocket

Additional features allow the Therm-a-Rest Parsec 0℉ Sleeping Bag to be customizable for warmth. The interior of the bag is made large enough that if it is a particularly cold night that sleeping in layers can be accomplished. Also, there are clips on the outside of the sleeping bag that allow a down blanket to attach to the top of the bag.  Again, this could be used for a particularly cold evening in the woods. On the bottom of the bag there are loops that fit a sleeping pad underneath. These are in place so that you don’t slide off of the sleeping pad at night.  

Therm-a-Rest Parsec 0F quilt and sleeping pad attachments

Field Testing the Therm-a-Rest Parsec 0℉ Sleeping Bag

I was very excited to test out the Therm-a-Rest Parsec 0℉ Sleeping Bag this spring here in Colorado. Our weather this year has been quite unpredictable, even for Colorado. We have had a few warm days with many cold days mixed in. These erratic weather patterns have made it challenging to prepare for sleeping in the backcountry. In the past I have shivered through nights where temperatures became unexpectedly chilly. Having a sleeping bag with a bit more warmth seemed perfect for spring camping in the Rockies.  

Cozy Morning in the Therm-a-Rest Parsec 0F Sleeping Bag

The Therm-a-Rest Parsec 0℉ Sleeping Bag was definitely the perfect choice for my first backpacking trip. The overnight temps were supposed to be in the mid 30 degree range. However, I woke up to a heavy frost and much closer to 20 than 30 degrees outside. I am so glad I was using the Therm-a-Rest Parsec 0℉ Sleeping Bag that night, as I was warm and comfortable. 


What I really like about the Therm-a-Rest Parsec 0℉ Sleeping Bag is how plush the bag is. When crawling into the bag you just sink in and the bag molds around the body. At this point the 800 degree down fill is incredibly noticeable and super comfy. It doesn’t take long to get nice and toasty in this bag. I am 5’10” and 175lbs and the medium bag fit perfectly. The bag was roomy and if I really needed to layer up I could put on some warm clothes.

The zippers are awesome. The tangle free zipper is great. It is nice not to have to worry about ruining the sleeping bag by zipping the nylon up into the zipper. This zipper would definitely be a game changer with kids. I have spent countless times undoing nylon fabric out of my son’s down sleeping bag.  

Although it was dry where I was camping, the morning was frosty and cold especially from the snow and rain from earlier in the week. Although much of my gear was damp it was noticeable that the sleeping bag did a nice job of repelling water. I really believe I would have seen this bag shine on a wet backpacking trip.  

Since the Therm-a-Rest Parsec 0℉ Sleeping Bag is a cold weather bag it does not pack down nearly as small as a bag with a warmer temperature rating would. Even though this bag is quite compressible it was a bit of a struggle to get it into my backpack. The compressed length was just a bit too long to get into the sleeping bag compartment easily.  

Maybe need to layer up for really cold nights

I definitely found this bag comfortable for the camping trips that I have been on this spring. However, I think it would be a bit of a stretch to use this sleeping bag as a dedicated winter sleeping bag. I could see really cold nights being a concern. With temps approaching the zero degree mark I would imagine additional blankets and layers might be necessary. I would feel more comfortable using the Therm-a-Rest Polar Ranger Sleeping bag that is rated to -20 degrees if I was planning on lots of cold winter camping.  

Specs on the Therm-a-Rest Parsec 0F Sleeping Bag taken directly from Therm-a-Rest

  • Color Larch
  • Weight 2lbs 6oz
  • Width 31.5 inches
  • Length 80 inch
  • Height 5.5 inches
  • Fits 72in
  • Girth at Shoulder 63 inches
  • Girth at Footbox 46 inches
  • Packed Dimensions 8” x 9”
  • Girth at Hips 58 inches
  • EN Comfort 14 F
  • EN Limit 0 F

Final thoughts on the Therm-a-Rest Parsec 0F Sleeping Bag

The Therm-a-Rest Parsec 0℉ Sleeping Bag is a great bag for those fringe season camping trips as well as some moderate winter camping. This 800 fill Nikwax Hydrophobic Down is great for all conditions and especially well suited in damp and wet environments. There was considerable effort placed into the design of this sleeping bag with many recycled materials used, a non binding zipper, and attachment points for a sleeping pad and a layered quilt. If you are looking for a sleeping bag that is perfect for those cold in between seasons this bag is for you. For more information visit or

Bennett Colvin: Bennett Colvin lives in Steamboat, Colorado and is an avid fisherman, hiker, skier, and outdoorsman. Bennett instructs fly fishing and runs youth fly fishing programs. He also is a professional fly tier and ties publicly at fly shops and expos.
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