Western Mountaineering UltraLite 20 Review – The Perfect Backpacking Companion?

Discover the Western Mountaineering UltraLite 20, a top-tier, lightweight sleeping bag offering exceptional warmth, durability, and packability for serious backpackers.
Western Mountaineering UltraLite 20

Western Mountaineering UltraLite 20

Explore the Ultimate Combination of Warmth, Weight, and Durability in the UltraLite 20 Sleeping Bag
The Western Mountaineering UltraLite 20 excels in providing lightweight, durable, and exceptionally warm sleeping solutions for three-season backpacking.


Warmth & Insulation
Packability & Weight
Comfort & Fit
Durability & Materials
Versatility & Features


  • Exceptional warmth-to-weight ratio
  • High-quality materials
  • Versatile temperature regulation
  • Compact and packable
  • Adjustable hood and draft collar
  • Variety of sizes


  • Price
  • Limited water resistance
  • Snug fit
  • Limited color options


Brief Overview

The Western Mountaineering UltraLite 20 sleeping bag is designed for serious outdoor enthusiasts who prioritize warmth, weight, and packability. Crafted for three-season use, this high-performance sleeping bag is perfect for backpacking, alpine climbing, and other activities where every ounce counts. With a temperature rating of 20°F (-6°C), it offers a balance between lightweight construction and the ability to keep you warm in chilly conditions.

Initial Impressions and Context of Testing

Upon first inspection, the UltraLite 20 immediately stands out for its meticulous craftsmanship and premium materials. The shell is made from a durable, yet lightweight, ripstop nylon that promises longevity without adding unnecessary weight. The bag is filled with 850+ fill power goose down, known for its superior insulation properties and compressibility.

Testing the UltraLite 20 in the rugged terrain of the Rocky Mountains provided a comprehensive evaluation of its performance. I embarked on a week-long backpacking trip, encountering a variety of weather conditions from cold, clear nights to unexpected rain showers. This diverse range of environments allowed for a thorough assessment of the sleeping bag’s capabilities, particularly in terms of warmth, comfort, and weather resistance.

My initial reaction was one of appreciation for the bag’s compact size when packed, which made it easy to stow in my backpack without taking up excessive space. The thoughtful design elements, such as the full-length zipper with a draft tube and the adjustable hood, immediately indicated that this sleeping bag was engineered with user comfort and protection in mind. As I prepared for my adventure, I was eager to see how these features would translate into real-world performance.

Technical Specifications

Key Features and Technology

The Western Mountaineering UltraLite 20 is packed with advanced features and cutting-edge technology designed to provide maximum comfort and efficiency in the backcountry. Here are some key highlights:

  • Temperature Rating: Rated for 20°F (-6°C), making it suitable for three-season use.
  • Fill Power: 850+ fill power goose down, offering exceptional warmth-to-weight ratio.
  • Weight: Approximately 1 lb 13 oz (0.82 kg) for the regular size, making it ultra-light and highly portable.

Design and Materials

Western Mountaineering has carefully selected top-tier materials to ensure durability, comfort, and performance. The design reflects a keen attention to detail:

  • Shell Fabric: Made from ExtremeLite™, a lightweight yet durable 12D ripstop nylon that protects the down insulation while maintaining breathability.
  • Lining: Smooth 15D nylon taffeta lining that feels comfortable against the skin and allows for easy movement inside the bag.
  • Insulation: Filled with high-loft 850+ fill power goose down, renowned for its superior insulating properties and compressibility.

Construction and Features

The UltraLite 20 incorporates several thoughtful design elements to enhance its functionality and user experience:

  • Continuous Baffles: The continuous baffle construction allows for even distribution of down and helps prevent cold spots.
  • Full-Length Zipper: The full-length YKK zipper with a locking mechanism ensures easy entry and exit, while the insulated draft tube along the zipper prevents heat loss.
  • Adjustable Hood: A contoured, adjustable hood that cinches tightly around the head to seal in warmth.
  • Draft Collar: An insulated draft collar with an elastic drawcord helps keep warm air in and cold air out.

Sizing Options

The Western Mountaineering UltraLite 20 is available in multiple sizes to accommodate different body types and preferences:

  • Regular: Fits up to 6 feet (183 cm).
  • Long: Fits up to 6 feet 6 inches (198 cm).
  • Short: Fits up to 5 feet 6 inches (168 cm).

Packability and Storage

One of the standout features of the UltraLite 20 is its exceptional packability:

  • Compressed Volume: Packs down to a remarkably small size, making it easy to fit into a backpack.
  • Storage Sack: Comes with a large storage sack to maintain loft when not in use and a stuff sack for easy packing on the trail.

These technical specifications highlight why the Western Mountaineering UltraLite 20 is a top choice for backpackers and climbers seeking a reliable, lightweight, and warm sleeping bag for their adventures.

Performance Evaluation

Fabric Performance

  • Breathability: The Western Mountaineering UltraLite 20 excels in breathability thanks to its ExtremeLite™ shell fabric. Even in slightly warmer conditions, the fabric manages moisture effectively, preventing a buildup of condensation inside the bag. This feature is particularly beneficial during high-intensity activities where sweating can be an issue.
  • Waterproofing: While the UltraLite 20 is not fully waterproof, it does offer significant water resistance. The DWR (Durable Water Repellent) finish on the shell helps repel light moisture and condensation. This was evident during my testing in a damp environment, where the bag managed to stay dry despite occasional contact with a wet tent wall.
  • Durability: The 12D ripstop nylon shell is impressively durable for its weight. After several nights of use, including rough handling and packing, the bag showed no signs of wear or tear. This durability ensures the sleeping bag will withstand the rigors of frequent backpacking trips.

Weather Resistance

The UltraLite 20 performs admirably across various weather conditions. Its 850+ fill power goose down provides excellent insulation, maintaining warmth even when temperatures dip below freezing. During a particularly cold night in the Rockies, the bag’s down insulation kept me warm and comfortable without the need for extra layers.

In mild to moderate weather, the sleeping bag’s ventilation features come into play. The full-length zipper can be partially or fully opened to regulate temperature, ensuring comfort across a range of climates. However, in wet conditions, it’s essential to pair the UltraLite 20 with a high-quality bivy sack or tent to ensure complete protection from moisture.

Practical Features

  • Zippers: The YKK full-length zipper is robust and operates smoothly without snagging. It includes a locking mechanism to prevent accidental unzipping during the night, and the draft tube along the zipper line minimizes heat loss.
  • Hood: The adjustable hood is a standout feature, designed to seal in warmth effectively. On particularly cold nights, cinching the hood tightly around the head provides additional insulation.
  • Draft Collar: The insulated draft collar with an elastic drawcord is another excellent addition, preventing warm air from escaping and cold air from entering the bag. This feature is particularly useful in maintaining a consistent internal temperature.
  • Stuff Sack and Storage Sack: The UltraLite 20 comes with a stuff sack for compact packing and a larger storage sack to maintain loft when the bag is not in use. This dual-sack system helps preserve the down’s insulating properties and prolong the bag’s lifespan.

Insulation and Warmth

The 850+ fill power goose down used in the UltraLite 20 is of premium quality, offering an exceptional warmth-to-weight ratio. During my testing, the sleeping bag provided consistent warmth in temperatures close to its lower limit of 20°F (-6°C). The continuous baffle construction ensures an even distribution of down, eliminating cold spots and enhancing overall thermal efficiency.

In conclusion, the Western Mountaineering UltraLite 20 delivers outstanding performance in terms of breathability, weather resistance, and practical features. Its lightweight yet durable construction, coupled with excellent insulation, makes it a reliable choice for backpackers and outdoor enthusiasts seeking a high-performance sleeping bag for three-season use.

Fit and Comfort

Sizing and Fit

The Western Mountaineering UltraLite 20 is available in three different sizes—Short, Regular, and Long—ensuring a tailored fit for a wide range of body types. The Regular size fits individuals up to 6 feet (183 cm), the Long size accommodates users up to 6 feet 6 inches (198 cm), and the Short size is designed for those up to 5 feet 6 inches (168 cm). This variety in sizing means that most users can find a version that fits them comfortably without feeling cramped or too spacious.

From my experience, the bag’s ergonomic design contours well to the body, providing a snug fit that maximizes thermal efficiency by minimizing the amount of air space inside the bag. This close fit is crucial for maintaining warmth, as it reduces the volume of air your body needs to heat.

Comfort During Various Activities

  • Sleeping Positions: One of the standout aspects of the UltraLite 20 is its comfort across different sleeping positions. Whether you’re a back sleeper, side sleeper, or stomach sleeper, the bag’s design accommodates various positions without compromising on warmth or comfort. As a side sleeper myself, I found the bag roomy enough to shift positions without feeling restricted.
  • Movement: Despite its snug fit, the UltraLite 20 offers enough room for some movement during the night. The nylon taffeta lining is smooth and allows for easy turning and shifting, which is particularly important for those who move frequently in their sleep.
  • Hood Design: The adjustable hood is another key feature contributing to overall comfort. Its contoured shape wraps around your head, providing insulation and comfort without feeling claustrophobic. The drawcords are easy to adjust, even in the dark, allowing you to tighten or loosen the hood as needed to regulate temperature.

Temperature Regulation

The UltraLite 20 excels in temperature regulation, an essential factor for maintaining comfort throughout the night. The full-length zipper can be opened partially or fully to increase ventilation during warmer nights. Conversely, on colder nights, the zipper’s draft tube and the insulated draft collar work together to seal in warmth effectively.

During my testing, the bag maintained a comfortable temperature even when outside conditions varied significantly. The ability to fine-tune the ventilation was particularly useful on nights when the temperature fluctuated.

Additional Comfort Features

  • Draft Collar: The draft collar, located around the neck area, adds an extra layer of insulation, preventing cold air from seeping in and warm air from escaping. This feature enhances comfort by maintaining a consistent internal temperature.
  • Foot Box: The foot box is well-designed, providing enough room for your feet to rest naturally without feeling constricted. This is especially important for taller users or those who prefer to sleep with their feet slightly elevated.

In conclusion, the Western Mountaineering UltraLite 20 offers an excellent balance of fit and comfort. Its thoughtful design accommodates various body types and sleeping positions while ensuring that you stay warm and comfortable throughout the night. The combination of high-quality materials, ergonomic design, and practical features makes it a top choice for backpackers and outdoor enthusiasts who prioritize comfort in their sleeping gear.

Pros and Cons


  • Exceptional Warmth-to-Weight Ratio: The 850+ fill power goose down provides superior insulation while keeping the weight minimal, making it ideal for backpacking and alpine climbing where weight is a critical factor.
  • High-Quality Materials: The use of 12D ripstop nylon for the shell and 15D nylon taffeta for the lining ensures durability and comfort. These materials are both lightweight and robust, promising longevity.
  • Versatile Temperature Regulation: The full-length YKK zipper allows for excellent temperature control. It can be fully opened for ventilation in warmer conditions or zipped up with the draft tube in place for maximum warmth on colder nights.
  • Compact and Packable: The UltraLite 20 packs down to a remarkably small size, which is a significant advantage for saving space in your backpack. The included stuff sack and storage sack enhance convenience and help maintain the loft of the down.
  • Adjustable Hood and Draft Collar: These features provide additional warmth and comfort, ensuring that heat is retained and cold air is kept out.
  • Variety of Sizes: With Short, Regular, and Long options, users of different heights can find a comfortable fit.


  • Price: The premium materials and high-quality construction come at a higher price point, which might be a significant investment for some users.
  • Water Resistance: While the DWR finish offers some protection against moisture, the bag is not fully waterproof. It requires additional protection, such as a bivy sack or a high-quality tent, in wet conditions.
  • Snug Fit: The close-fitting design, while excellent for thermal efficiency, might feel too restrictive for users who prefer more space or tend to move around a lot during sleep.
  • Limited Color Options: The UltraLite 20 is typically available in a limited range of colors, which may not appeal to users looking for more variety.

In summary, the Western Mountaineering UltraLite 20 offers a host of advantages that make it a top-tier choice for serious outdoor enthusiasts. However, potential buyers should consider the higher cost and the need for additional waterproofing measures when making their decision. Despite these minor drawbacks, the overall performance and quality of the UltraLite 20 make it a worthy investment for those seeking a reliable, lightweight, and warm sleeping bag for their adventures.

Comparative Analysis

When comparing the Western Mountaineering UltraLite 20 to the Feathered Friends Swallow UL 20 and the Kelty Cosmic Down 20, several differences and similarities stand out.

The Feathered Friends Swallow UL 20 is another top-tier option for serious backpackers and mountaineers. Similar to the UltraLite 20, it uses 900+ fill power goose down, providing excellent warmth-to-weight ratio. The Swallow UL 20 also boasts a durable and lightweight shell made from Pertex® Endurance fabric, which offers superior water resistance compared to the UltraLite’s 12D ripstop nylon. However, the Swallow UL 20 is slightly heavier and bulkier when packed, making it less ideal for ultralight backpackers who prioritize minimal weight and pack size.

On the other hand, the Kelty Cosmic Down 20 is a more budget-friendly option that offers good performance for its price. It uses 550 fill power down, which is significantly lower in insulation quality compared to the UltraLite 20’s 850+ fill power goose down. This makes the Cosmic Down 20 heavier and bulkier, with less compressibility. While it does offer decent warmth and comfort, it cannot match the high performance and lightweight design of the UltraLite 20. Additionally, the materials used in the Cosmic Down 20 are not as premium, resulting in a less durable product overall.

In conclusion, while the Feathered Friends Swallow UL 20 offers comparable warmth and slightly better water resistance, it comes with added weight and bulk. The Kelty Cosmic Down 20, though more affordable, cannot compete with the UltraLite 20’s premium materials and superior insulation. For those who can afford the investment, the Western Mountaineering UltraLite 20 remains a top choice for its exceptional balance of warmth, weight, and durability.


The Western Mountaineering UltraLite 20 is a standout choice for serious backpackers and outdoor enthusiasts who demand high performance from their gear. Its exceptional warmth-to-weight ratio, courtesy of the 850+ fill power goose down, combined with premium materials and thoughtful design features, ensures it provides reliable comfort and insulation in a variety of conditions. Despite its higher price point and the need for additional waterproofing in wet environments, the UltraLite 20’s compact packability, durability, and superior temperature regulation make it a worthy investment for those seeking a lightweight yet robust sleeping bag.

Ideal for three-season use, this sleeping bag is best suited for activities where weight and pack size are critical, such as long-distance backpacking and alpine climbing. If you prioritize quality, performance, and reliability, the Western Mountaineering UltraLite 20 is an excellent addition to your outdoor gear arsenal.

Further reading