Sea to Summit Spark 45 Review – The Ultimate Ultralight Sleeping Bag?

Sea to Summit Spark 45: An ultralight, compact sleeping bag with excellent warmth-to-weight ratio, perfect for three-season backpacking.
Sea to Summit Spark 45

The Sea to Summit Spark 45

Uncover the Performance and Features of Sea to Summit's Premier Ultralight Sleeping Bag
The Sea to Summit Spark 45 is an ultralight, compact, and durable sleeping bag ideal for three-season backpacking, offering excellent warmth-to-weight ratio and packability.


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


  • Ultra-lightweight
  • Compact packability
  • Excellent warmth-to-weight ratio
  • Durable
  • Adjustable hood and foot box
  • Breathability and moisture management


  • High price point
  • Tapered fit
  • Limited temperature range
  • Zipper length
  • Specific use case


Brief Overview

The Sea to Summit Spark 45 is a high-performance sleeping bag designed for ultralight backpackers and outdoor enthusiasts who prioritize minimal weight without compromising on warmth and comfort. Engineered for those who venture into the wild with a focus on efficiency and packability, the Spark 45 stands out as a premium option in the ultralight sleeping bag market. This sleeping bag is part of Sea to Summit’s renowned Spark series, known for its exceptional warmth-to-weight ratio and compact size.

Initial Impressions and Context of Testing

Upon unboxing the Sea to Summit Spark 45, the first thing that strikes you is its remarkably compact size and lightweight nature. It feels almost too light to provide significant warmth, yet the high-quality materials and meticulous construction immediately convey a sense of reliability and performance. The Spark 45 packs down to an impressively small volume, making it an ideal choice for minimalist adventurers who need to save space in their backpacks.

Testing the Spark 45 took place over a series of multi-day backpacking trips in the varied terrains and climates of the Pacific Northwest. From damp, chilly coastal trails to high-altitude alpine environments, the sleeping bag was subjected to a range of conditions to evaluate its versatility and effectiveness. Initial impressions were overwhelmingly positive, with the bag’s compactness and ease of packing standing out as key benefits.

Technical Specifications

Key Features and Technology

The Sea to Summit Spark 45 is designed with cutting-edge technology to ensure optimal performance for ultralight backpacking. Some of the standout features include:

  • Ultra-Dry Down™: The Spark 45 is insulated with 850+ fill power Ultra-Dry Down™, a water-repellent down treatment that helps maintain loft and insulating properties even in damp conditions.
  • Lightweight Construction: Advanced materials and construction techniques reduce weight without compromising durability or warmth.
  • Tapered Mummy Shape: This design minimizes weight and maximizes thermal efficiency by reducing excess air space inside the bag.

Design and Materials

The Spark 45’s design and materials are meticulously chosen to balance weight, warmth, and durability:

  • Shell and Lining Fabric: The outer shell is made from 10D Nylon, which is exceptionally lightweight yet strong. The inner lining is 7D Nylon, providing a soft and comfortable feel against the skin.
  • Zipper: A full-length, lightweight YKK zipper with anti-snag design ensures easy entry and exit without adding unnecessary weight.
  • Construction: The sleeping bag features a sewn-through construction, which is a lightweight method of keeping the down insulation evenly distributed.

Dimensions and Weight

  • Regular Size: Fits users up to 6 feet (183 cm) tall.
    • Weight: Approximately 12 ounces (340 grams).
    • Packed Size: Compressed volume of 1.5 liters.
  • Long Size: Fits users up to 6 feet 6 inches (198 cm) tall.
    • Weight: Approximately 14 ounces (397 grams).
    • Packed Size: Compressed volume of 1.7 liters.

Temperature Rating

  • Comfort Range: 46°F (8°C)
  • Lower Limit: 39°F (4°C)
  • Extreme Rating: 10°F (-12°C)

These ratings make the Spark 45 ideal for three-season use in moderate climates. However, layering with additional clothing can extend its usability into cooler conditions.

Additional Features

  • Hood Design: A snug, adjustable hood with drawcords helps retain warmth around the head.
  • Foot Box: Anatomically shaped foot box provides more room for feet, enhancing comfort and insulation.
  • Compression Sack: Comes with an Ultra-Sil™ Nano compression sack for easy packing and minimal bulk.

In summary, the Sea to Summit Spark 45 combines advanced materials and thoughtful design to deliver an ultralight sleeping bag that excels in performance, making it a top choice for serious backpackers and outdoor adventurers.

Performance Evaluation

Fabric Performance

Breathability: The Sea to Summit Spark 45 excels in breathability, thanks to its high-quality 10D Nylon shell and 7D Nylon lining. These materials effectively manage moisture, ensuring that condensation buildup inside the bag is minimized. This feature is crucial for maintaining comfort and preventing a clammy feeling during warmer nights or when used in humid environments.

Waterproofing: While the Spark 45 is not fully waterproof, its Ultra-Dry Down™ insulation provides significant water resistance. The down treatment helps repel moisture, maintaining loft and insulating properties even when exposed to damp conditions. This feature enhances the sleeping bag’s performance in environments where moisture is a concern, such as dewy mornings or light rain.

Durability: Despite its ultralight design, the Spark 45 is remarkably durable. The 10D Nylon shell offers a strong resistance to abrasions and tears, which is essential for withstanding the rigors of backcountry use. The high-quality stitching and construction further contribute to the bag’s longevity, ensuring it can endure frequent packing and unpacking.

Weather Resistance

Temperature Regulation: The Spark 45 is designed for three-season use, with a comfort range down to 46°F (8°C) and a lower limit of 39°F (4°C). In testing, the bag provided consistent warmth in a variety of weather conditions, from cool alpine nights to temperate coastal mornings. The Ultra-Dry Down™ insulation efficiently traps heat, providing reliable warmth without excessive bulk.

Wind Resistance: The tightly woven 10D Nylon shell offers excellent wind resistance, reducing the chill factor in breezy conditions. This feature is particularly beneficial when camping in exposed areas where wind can significantly impact warmth and comfort.

Practical Features

Hood Design: The adjustable hood of the Spark 45 is a standout feature, providing a snug fit around the head to retain warmth. The drawcords are easy to adjust, allowing for quick modifications depending on the weather conditions.

Foot Box: The anatomically shaped foot box is designed to provide extra space for your feet, enhancing overall comfort and insulation. This design helps keep your feet warm and reduces the risk of cold spots, which is a common issue in less thoughtfully designed sleeping bags.

Zipper Functionality: The full-length YKK zipper with an anti-snag design operates smoothly and reliably. This feature is crucial for easy entry and exit, especially in the dark or when you’re tired after a long day of hiking. The zipper’s draft tube also helps prevent heat loss through the zipper, maintaining the bag’s overall thermal efficiency.

Compression and Packability: One of the most impressive aspects of the Spark 45 is its ability to compress into a very small volume. The included Ultra-Sil™ Nano compression sack makes it easy to pack the bag down to a compact size, saving valuable space in your backpack. This feature is particularly appreciated by ultralight backpackers who need to maximize every inch of their pack.

In conclusion, the Sea to Summit Spark 45 delivers outstanding performance across various aspects, from fabric breathability and water resistance to practical features like the hood and foot box design. Its lightweight and compressible nature make it a top choice for ultralight backpackers who demand high performance in a minimal package.

Fit and Comfort

Sizing and Fit

The Sea to Summit Spark 45 is designed with a tapered mummy shape, which helps minimize weight while maximizing thermal efficiency. The bag comes in two sizes: Regular, which fits users up to 6 feet (183 cm) tall, and Long, which accommodates users up to 6 feet 6 inches (198 cm) tall. This range of sizes ensures that most backpackers can find a good fit. The tapered design hugs the body, reducing dead air space and allowing the insulation to work more effectively.

Comfort During Various Activities

Sleeping Position Versatility: Despite its snug fit, the Spark 45 offers enough room to move comfortably within the bag. Whether you’re a back, side, or stomach sleeper, the bag’s design allows for some movement without feeling too restrictive. The anatomically shaped foot box provides extra space for your feet, which is especially beneficial for side sleepers who often find traditional mummy bags too constricting.

Temperature Regulation: The Ultra-Dry Down™ insulation not only provides warmth but also adapts well to varying conditions. On warmer nights, the full-length zipper can be unzipped to allow for better ventilation, preventing overheating. Conversely, on cooler nights, the draft tube along the zipper and the snug hood help retain warmth, ensuring a comfortable sleep.

Material Comfort: The 7D Nylon lining feels soft and smooth against the skin, which enhances overall comfort. Unlike some sleeping bags that can feel sticky or clammy, the Spark 45’s lining promotes a pleasant sleeping environment. Additionally, the high-quality down insulation feels plush and cozy, further contributing to a restful night’s sleep.

Adjustable Features

Hood Adjustments: The Spark 45 features a well-designed hood with adjustable drawcords that allow you to cinch it tightly around your head on cold nights. This feature is essential for preventing heat loss and keeping your head warm. The drawcords are easy to use, even with gloves on, making adjustments simple and quick.

Zipper Convenience: The YKK zipper not only ensures durability but also operates smoothly, allowing for easy entry and exit from the sleeping bag. The anti-snag design prevents frustrating catches, and the zipper draft tube helps keep out cold drafts, maintaining the bag’s thermal efficiency.

Overall Comfort

The Sea to Summit Spark 45 strikes an excellent balance between lightweight design and user comfort. Its tapered shape and efficient insulation make it warm and cozy, while the thoughtful design features ensure that it doesn’t feel restrictive. The ability to move freely, adjust the hood, and use the zipper easily all contribute to a highly comfortable sleeping experience, whether you’re camping in mild summer weather or cooler spring and fall conditions.

In summary, the Spark 45 is designed to offer maximum comfort without compromising its ultralight nature, making it a top choice for backpackers who need a reliable and comfortable sleeping bag for a range of outdoor adventures.

Pros and Cons


Ultra-Lightweight: The Sea to Summit Spark 45 is exceptionally lightweight, with the Regular size weighing just around 12 ounces (340 grams). This makes it an ideal choice for ultralight backpackers who need to minimize pack weight without sacrificing warmth.

Compact Packability: The sleeping bag compresses down to a very small size, fitting easily into its Ultra-Sil™ Nano compression sack. This feature is particularly beneficial for those with limited pack space.

Excellent Warmth-to-Weight Ratio: Thanks to the 850+ fill power Ultra-Dry Down™, the Spark 45 provides significant warmth relative to its weight. It maintains good thermal efficiency, keeping users comfortable in temperatures as low as 39°F (4°C).

Durability: Despite its lightweight design, the 10D Nylon shell and 7D Nylon lining are durable and can withstand the rigors of backcountry use. The high-quality construction ensures longevity.

Adjustable Hood and Foot Box: The adjustable hood and anatomically shaped foot box enhance overall comfort, providing a snug fit that helps retain warmth while allowing some freedom of movement.

Breathability and Moisture Management: The materials used in the Spark 45 offer excellent breathability, reducing the risk of condensation buildup and ensuring a dry, comfortable sleep environment.


High Price Point: The Spark 45 is on the higher end of the price spectrum for ultralight sleeping bags. While its features and performance justify the cost, it may be out of reach for budget-conscious backpackers.

Tapered Fit: The mummy-style tapered fit, while efficient for warmth, may feel too restrictive for some users, especially those who prefer a roomier sleeping bag.

Limited Temperature Range: While suitable for three-season use, the Spark 45 may not provide enough warmth for extremely cold conditions without additional layering. Users venturing into colder environments might need a more heavily insulated bag.

Zipper Length: The full-length zipper is convenient but can sometimes allow for slight drafts if not properly aligned with the draft tube. Ensuring the zipper is fully sealed is essential for maintaining warmth.

Specific Use Case: The ultralight and compact nature of the Spark 45 is perfect for backpacking but might not be necessary for car camping or other types of camping where weight and space are less of a concern.

In summary, the Sea to Summit Spark 45 excels in lightweight design, packability, and warmth, making it a top choice for ultralight backpackers. However, its high price and specific fit might be considerations for potential buyers.

Comparative Analysis

When comparing the Sea to Summit Spark 45 with the Feathered Friends Swallow UL 20 and the Kelty Cosmic Down 20, several differences and similarities stand out, highlighting the strengths and potential limitations of each sleeping bag in the ultralight backpacking category.

Feathered Friends Swallow UL 20: The Swallow UL 20 is renowned for its exceptional warmth-to-weight ratio and high-quality construction. It uses 950+ fill power goose down, which provides superior insulation compared to the 850+ fill power down in the Spark 45. This makes the Swallow UL 20 a warmer option, suitable for colder temperatures, with a lower limit rating around 20°F (-6°C). However, it is also heavier, weighing approximately 27 ounces (765 grams), which is more than double the weight of the Spark 45. This makes the Swallow UL 20 a better choice for those needing more warmth but willing to carry a bit more weight.

Kelty Cosmic Down 20: The Cosmic Down 20 is a more budget-friendly option compared to both the Spark 45 and the Swallow UL 20. It features 600 fill power down, which is significantly lower than the fill power of the other two bags, resulting in a heavier weight (approximately 41 ounces or 1162 grams) and bulkier pack size. Its temperature rating is also around 20°F (-6°C), making it warmer than the Spark 45 but less efficient in terms of weight-to-warmth ratio. The Cosmic Down 20 is a solid option for those new to backpacking or on a tighter budget, offering decent performance without the premium price tag of the Spark 45.

In summary, the Sea to Summit Spark 45 is an excellent ultralight option for moderate temperatures, excelling in weight and packability. The Feathered Friends Swallow UL 20 offers superior warmth at the cost of additional weight, making it ideal for colder conditions. The Kelty Cosmic Down 20 provides a budget-friendly alternative with reasonable performance but at a heavier weight and bulkier size. Each bag serves different needs, making it essential for backpackers to prioritize their specific requirements when choosing the right sleeping bag.


The Sea to Summit Spark 45 is a standout choice for ultralight backpackers and outdoor enthusiasts who demand high performance in a compact and lightweight package. With its impressive warmth-to-weight ratio, excellent packability, and durable construction, the Spark 45 excels in three-season use, offering reliable comfort and insulation in moderate conditions. While its high price point and tapered fit may be considerations for some, the advanced materials and thoughtful design features justify the investment for serious backpackers. The Spark 45 is particularly well-suited for minimalist adventurers who need to maximize every inch of their pack space without compromising on warmth and comfort. Overall, the Sea to Summit Spark 45 provides exceptional value for those seeking a top-tier ultralight sleeping bag for a variety of outdoor adventures.

Further reading