Gear Review: Marmot Phase 20 Sleeping Bag

The Marmot Phase 20 is made for hikers pushing into ultralight territory who don’t want to sacrifice the warmth and comfort of a good night’s sleep. The 850+ power goose down lofts high for warmth, and the Pertex 10D nylon ripstop is like silk against the skin.

Marmot Phase 20 At-a-Glance

Price: $459 MSRP.
Weight: 1 pound, 7.3 ounces (men’s regular).
Insulation: 850+ power down insulation with Down Defender to fend off moisture.
Shell: Pertex 10D nylon ripstop.
Zipper: Full length, two-way.
Circumference: Shoulders, 60 inches; hips, 58 inches; regular length.
Length: 72 inches, regular; 78 inches, long.

Temperature Rating (Fahrenheit): 
18.5: Lowest temperature limit for men.
29.5: For women to be comfortable.
Minus 13.7: Temperature at which the bag should be used only in an emergency.

Marmot uses the European Norm to test the warmth of sleeping bags.


Stuff size: 7.5 inches by 16 inches.
Color: Arctic navy outside, Mykonos blue interior.

The women’s Phase 20 is available here.

Circumstance of Review

My first reaction to the Phase 20? Plush. My second? So light! But it was the cool nights in Connecticut and a long trip on the Long Trail in Vermont that sold me. The warmth-to-weight ratio is amazing: 20-degree warmth in a bag that weighs 1.7 pounds. I slept in the Phase 20 on cool May nights in Connecticut, and surprisingly cold nights on the Long Trail. A downpour during the night in Vermont left moisture inside my tent and on the outside of the Phase 20. I stayed warm and dry inside the bag despite the moisture inside my tent.


Fill: The Phase 20 has 14.1 ounces of 850+ fill down treated with Down Defender, what Marmot calls an “insurance policy for down garments and sleeping bags.” The down is treated with a hydrophobic layer that Marmot says keeps the bag drier ten times longer than untreated down in damp conditions, maintains 150% more loft than untreated down in damp weather, and dries 30% faster than untreated down.

Fill power is important for ultralight gear; a 600-fill down bag may keep you warm to 20 degrees, but it’s going to take more down fill to reach that temperature rating, and thus be heavier. So the higher the fill power, the better the warmth-to-weight ratio.

Warmth: Marmot uses the European Norm (EN) standard for testing temperature ratings. Sample sleeping bags are sent to Norway for testing, and Marmot puts the EN rating on bags (required in Europe, voluntary in the US). The tag shows three temperature ranges: comfort limit, based on a woman having a comfortable night’s sleep (29.5F); lower limit, based on a man at the lowest temp to have a comfortable night’s sleep (18.5F); and extreme rating (minus 13.7F), when the bag is to be used only in an emergency.

Comfort: I’m 5’10” and 165 pounds, and the Phase 20 has room for me to move. And I do move a lot during the night. Left side, right side, back. The tapered foot box still gave me room to move my feet and legs.

Material: The Pertex fabric is a gold standard for quality sleeping bags and clothing. Both the shell and liner are made with ten-denier Pertex Quantum TGL fabric, a tightly woven material that creates a light and soft fabric that allows the insulation to fully loft, traps still air, and improves the efficiency of the insulation. Conversely, in performance clothing, a more open weave provides a balance of breathability and wind resistance.

For gear freaks, denier fiber thickness ranges from one (considered ultralight) to ten (the standard for most outdoor gear) to 20 (the width of human hair). Fabrics with a low-denier count tend to be sheer, soft, and silky. The durable water repellent (DWR) finish of the Phase 20 sheds light rain and snow to provide additional weather protection. In sum, the fabric is lightweight and packable, soft to the touch, and windproof to retain warmth.

Zipper: The bag has a full-length, locking YKK left-side two-way zipper with anti-snag slider backed by an insulated draft tube. Complaints abound on the internet about the zipper snagging easily, but I found that putting a finger between the zipper and the draft tube provided a smooth zip. And don’t forget that two-way, full-length zippers are a rarity for bags this light. The two-way zipper provides ventilation in the footbox, a nice feature that I liked on warmer nights.

The two-way zipper allows air into the sleeping bag for ventilation.

Baffles: The smooth, curved baffles are designed to reduce down shifting and cold spots.

Stash pocket: Nice for stowing a watch, a phone, or something small. And surprising for a bag this light.

Room for a cell phone in the stash pocket.

Footbox: Narrow to save weight, but not constricting.

Shoulders: Plenty of room to move around. 60-64 inches standard width for the men’s bag.

Hood: I liked the straight cut of the hood, and the draft collar nestled comfortably around my face. The drawstring was easy to work with one hand. And I liked the curved zipper at the hood that creates a boxy opening for your face when fully zipped.

Warmth to weight: A one-pound, seven-ounce bag providing warmth to 20 degrees? Few bags match that ratio.

Add-ons: A stuff sack and storage sack are included, though the stuff sack is not a compression bag. There are two hang loops at the foot of the bag.

Corporate responsibility: Marmot follows Bluesign guidelines, which are intended to reduce the impact of manufacturing on people and the environment. Marmot uses down only from geese that have been killed for food, and requires suppliers to certify that they are in compliance with the company’s animal rights policies.

Point of origin: The shell is made in China and the bag is filled and finished in Rohner Park, CA.

Warranty: Marmot’s warranty covers manufacturing defects.


Weight: Light without sacrificing comfort.

Warmth: I was comfortable in the low 30s without pulling the hood fully closed. I could see this bag easily keeping me warm down to 20.


None: I really couldn’t find anything to dislike about this bag. It was comfortable, my air pillow fit snugly inside the hood, and it shed moisture and dried quickly.

Overall / Value

Price: High. But ultralight and comfort don’t come cheaply, unfortunately. And neither does quality gear you can expect to last for years.

Durability: Marmot guarantees every product it makes to be free of manufacturer defects.

Warmth: Expect the Phase 20 to keep you warm from 20 to 40 degrees. Anything above 40 and you’ll want to sleep on top of the bag.

Packability: Insanely compact.

Comfort, but at a Cost

The Marmot Phase 20 is a comfortable, packable, warm bag that does everything you would expect a sleeping bag to do: give you a good night’s sleep. The price is high, but almost $100 less than some other bags in this category. It’s a bag I expect to carry for years on trail.

Comparable 20-Degree Bags

Big Agnes Hitchens UL 20
Weight: 1 pound, 11 ounces (regular)
MSRP: $530
Fill: 850 fill down.

Rei Igneo 17 (men’s)
Weight: 1 pound, 15 ounces (regular)
MSRP: $299
Fill: 700 fill down

Feathered Friends Swift UL 20
Weight: 1 pound, 13 ounces (regular)
MSRP: $539
Fill: 950+ fill down

Shop the Phase 20 Here

This product was donated for purpose of review.

Affiliate Disclosure

This website contains affiliate links, which means The Trek may receive a percentage of any product or service you purchase using the links in the articles or advertisements. The buyer pays the same price as they would otherwise, and your purchase helps to support The Trek's ongoing goal to serve you quality backpacking advice and information. Thanks for your support!

To learn more, please visit the About This Site page.

Comments 4

  • Stefan Biderman : Oct 1st

    Hi, appreciated your review. Interesting to learn you can make the zipper work, just handling it the right way.

    But as far as I remember from reviews this bag does not have a full-length zipper, and it certainly doesn´t look like a full-length zipper on your pictures either. A full-length zipper extends further than that into the foot section.

    With kind regards,


    • Hugh Owen : Oct 7th

      Stefan, thanks for your comments. I appreciate it when readers pass along information I might have missed for a review.
      Marmot does call the Phase 20 zipper full length.
      “Full Length Locking YKK Two Way Zipper with Anti-Snag Slider reduces fabric snagging.”

  • Christopher latimer : Sep 27th

    Just a quick one, I’ve done my research and have a phase 20 on order. I’ve noted the lack of compression sack and plan on picking a sea to summit ultra sil event dry bag. My question is what size of compression sack should I go for:
    13 x 25 cm (XXS); 15 x 34 cm (XS); 18 x 40 cm (S); 20 x 46 cm (M); 23 x 50 cm (L)
    The above are un compressed so I need to get one that the bag will fit into before I compress.
    I hope you can help.

    • Hugh Owen : Sep 27th

      Christopher, I use a small, 10L, 18cm by 40cm Sea To Summit Ultra-Sil Compression Dry Sack for the Marmot Phase 20. Hope that helps.


What Do You Think?