Reviews You Can Rely On

Marmot Phase 20 Review

An ultra-premium bag that's spoiled by a less-than-premium zipper
marmot phase 20 backpacking sleeping bag review
Credit: Marmot
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Price:  $486 List
Manufacturer:   Marmot
By Jack Cramer ⋅ Review Editor  ⋅  Apr 30, 2021
  • Warmth - 20% 8.0
  • Weight - 20% 8.0
  • Comfort - 20% 6.0
  • Packed Size - 15% 6.0
  • Versatility - 15% 7.0
  • Features & Design - 10% 5.0

Our Verdict

Our first impression of Marmot Phase 20 was that it seemed every bit as good as the exquisite bags from Feathered Friends and Western Mountaineering. Its down is as lofty, its fabric as smooth, and it even weighs a tiny bit less. These qualities combine into a bag that's similarly cozy with a comparably excellent warmth-to-weight ratio. Hands-on testing, however, revealed a zipper that is far inferior. Its ¾-length is simply inadequate for venting excess heat on warmer nights. More importantly, the zipper's tiny size causes it to snag on the adjacent fabric without mercy. This is disappointing for a bag that costs so much and performs so well in other areas.
Great loft
High warmth-to-weight ratio
Cozy hood
Convenient interior stash pocket
Frustrating zipper
Narrow fit
Limited ventilation options

Our Analysis and Test Results

The Phase 20 offers exceptional loft and high-quality materials. In many ways, its performance warrants an award. However, its small, infuriating zipper undermines any accolades. Many online customer reviews confirm this zipper is a popular problem. We sincerely hope Marmot fixes the zipper soon so this bag's otherwise outstanding performance can receive the recognition it deserves.

Performance Comparison

marmot phase 20 backpacking sleeping bag review - the marmot phase 20 features the same wonderful down and quality...
The Marmot Phase 20 features the same wonderful down and quality fabric as the top-scoring sleeping bags. It's finicky zipper spoils otherwise stellar performance.
Credit: Jack Cramer


The Phase 20 is one of the warmest 3-season bags we tried. Its 16.3 ounces of lofty 850 fill power down earn it a 22° EN lower limit temperature rating. It also includes a hood that cinches down to a tiny, but comfortable, opening to seal heat inside. Overall, our testers thought it felt a little warmer than its EN rating.

marmot phase 20 backpacking sleeping bag review - in our tests, the phase 20 seemed to provide a little more warmth...
In our tests, the Phase 20 seemed to provide a little more warmth than is 22F lower limit temp rating.
Credit: Jack Cramer


This bag features thin Pertex Quantum shell fabric and a tiny ¾-length zipper to minimize weight. On our scale, it weighed in at 1.65 pounds for a size Long. This compares favorably with other ultra-premium bags. We believe it provides nearly the same awesome warm-to-weight performance as its Western Mountaineering and Feathered Friends competitors, which share the gold standard in this aspect.

marmot phase 20 backpacking sleeping bag review - this bag is spacious enough in its shoulder dimensions, but some of...
This bag is spacious enough in its shoulder dimensions, but some of our testers complained of feeling cramped inside the narrower foot of the bag.
Credit: Jack Cramer


The Phase 20 features silky smooth interior fabric and lofty premium down. Together they create an incredibly comfortable interior feel. We also love this bag's hood, which unlike a lot of others, remained comfy even when cinched down fully. The narrow dimensions, however, harmed its overall score. The lower leg area, in particular, felt constrictive and so much so that we can't recommend this bag for side sleepers.

marmot phase 20 backpacking sleeping bag review - the phase 20 compresses reasonably small. however, the simple...
The Phase 20 compresses reasonably small. However, the simple drawstring stuff sack that it's sold with is not capable of fully compressing it.
Credit: Jack Cramer

Packed Size

Despite its low weight, the Phase 20 didn't display an especially small packed size. Using a third-party compression sack, we measured its minimum compressed volume at 8.9 liters. This is markedly larger than the most compact bags but on par with other comparably warm models. Unfortunately, this bag doesn't come with an effective compression sack so you'll need to upgrade from its simple stuff sack to enjoy its maximum compressibility.

marmot phase 20 backpacking sleeping bag review - all down bags will lose a substantial portion of their insulative...
All down bags will lose a substantial portion of their insulative power if they get wet. Hopefully, you get a sunny day to dry them back out.
Credit: Jack Cramer


Like some of the other ultra-premium down bags, the Phase 20's down is contained inside continuous horizontal baffles. These allow you to move feathers to the top or underside of the bag to adjust the amount of insulation. Its ¾-length zipper, however, gives you only mediocre opportunities to vent excess heat on warmer nights. Together these features counterbalance each other to give this bag moderate versatility across a range of temperatures.

Features and Design

This bag includes a convenient internal stash pocket for keeping your phone or headlamp batteries warm. As we mentioned before, we also really love its hood design and drawstring closure.

marmot phase 20 backpacking sleeping bag review - the small zipper seen here relies on a grooved, u-shaped slide that...
The small zipper seen here relies on a grooved, U-shaped slide that seemed very prone to snagging in our tests.
Credit: Jack Cramer

The main zipper, however, was a consistent source of frustration. To save weight, it is particularly small, but this seems to make it prone to snagging. Several online customer reviews also describe the zipper slide outright breaking or zipper snags that caused the thin fabric next to the zipper to tear. We didn't observe these problems in our tests, but they are concerns you should be aware of.


The Phase 20 is as expensive as other down bags with 850 or more fill power. For this price, you certainly get a high-quality bag that is exceptionally warm and light. The drawbacks, however, with comfort and the frustrating zipper are hard to look past. For these reasons, we believe there are several similar bags that provide an overall better value.

marmot phase 20 backpacking sleeping bag review - the internal stash pocket on this bag is a little to small for most...
The internal stash pocket on this bag is a little to small for most modern smartphones.
Credit: Jack Cramer


It's clear that the Marmot Phase 20 wants to compete with the best sleeping bags out there. With its 850 fill power down and feather-light fabric, it offers similar warmth and lightweight performance as the nicest Feathered Friends and Western Mountaineering bags. However, the Phase 20's uncomfortably narrow dimensions and finicky zipper ultimately spoil the potential competition. In our direct comparison tests, the Feathered Friends Hummingbird and Western Mountaineering MegaLite both proved themselves to be better designed at a similar price point.

Jack Cramer
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