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Ascent Down Sleeping Bag (25°F, 15°F & 0°F)


$349.00 – $469.00

Sleeping Bag Temperature Ratings Explained

The EN Rating scale is a scientific test to determine the warmth of a sleeping bag. The test produces a Lower rating (for male sleepers) and a Comfort rating (for female sleepers). Both are listed in the features table on the product page.

A unisex sleeping bag with a Lower limit of 23ºF means a man should be comfortable down to air temperatures of 23ºF. The same bag will also have a Comfort limit, in the realm of 32°F, so a woman would be comfortable down to an air temperature of 32ºF. These ratings require a sleeping mat with an R-Value appropriate for expected ground temperatures – without this, the sleeping bag itself is unlikely to keep the sleeper warm enough.

A variety of factors impact sleeping bag warmth - the above temperatures are merely guidelines, not guarantees. It’s important to think of a sleeping bag, an appropriately insulating sleeping pad and a liner as a sleep system. For example - if you plan on sleeping in nighttime air temperatures of 27ºF / -3°C, choose a bag with a gender-appropriate rating of 23°F / -5°C, plus a sleeping mat with an R-Value of 2.5 to 3, and consider a Reactor thermal liner.


The Ascent™ down mummy sleeping bag redefines what versatile means in a sleep system. Complex construction and high-quality down keep you warm when it’s cold outside, while the triple-zipper Free-Flow Zip™ system ensures you stay cool and ventilated when the weather warms.

Shaped to allow a natural sleeping position for comfort, the Ascent is light and compact enough to go everywhere your adventures may take you.

Is this down mummy sleeping bag…?

  • Warm enough for cold-weather use? Yes. The high-lofting down, technical hood, oversized draft tubes, and draft collar make the Ascent 25°F and 15°F true 2.5 – 3 season bags. For colder weather, you might choose the Ascent 0°F model and pair it with a high R-Value sleeping mat like the Comfort Light Insulated.

  • Really cool in summer temperatures? Yes. The Free-Flow Zip system means separate zippers on your left and right side and in the foot box. Open them for ventilation or to turn the Ascent into a fully-flat comforter.

  • Able to be zipped to another sleeping bag? The main side zipper can be zipped to the Sea to Summit Women’s Altitude, Journey and Venture sleeping bags – Regular and Long bags have the same side zipper length.

Read up on how the shape, construction and down quality of a sleeping bag will affect how well you sleep HERE 


Best Use

  • Backpacking


  • 2.5 Season: 25°F (comfort range 25°F to 70°F)
  • 3 Season: 15°F (comfort range 15°F to 65°F)
  • Winter: 0°F (comfort range 0°F to 60°F)


  • More room between hips and knees to allow you to sleep in a natural position without compressing the down insulation and creating cold spots. Far more comfortable than narrow mummy bags for most sleepers.


  • ULTRA-DRY Down 750+ Loft 90% Down Cluster Premium Duck Down certified Responsible Down Standard (RDS)
  • Free-flow zipper system: full-length YKK® #5 main side zip, half-length opposite side zip, and foot zip provides unparalleled ventilation and use as a comforter.
  • Vertical baffles over the chest to prevent down shifting as you roll over in your sleep.
  • Shaped hood, oversized draft collar, and zipper draft tube keep the cold out and the warmth in.
  • Internal pocket for phone / GPS / valuables.
  • Form a snug double sleeping bag by zipping to any Altitude™, Journey™ or Venture™ sleeping bag.
  • Includes lightweight Ultra-Sil™ compression bag and storage cell.

Technical Features

750+ Loft Ultra-Dry Down™

The second highest-lofting down used in any of Sea to Summit’s sleeping bags. 750+ Fill Power indicates that one ounce (30g) of down will re-expand to over 750 cubic inches after compression. Higher loft means that less down can be used to achieve the same temperature rating – important for performance sleeping bags. The loft and down quality/composition are independently tested by the International Down and Feather Laboratory (IDFL) – a copy of the certification is supplied with every Sea to Summit sleeping bag.


The down is responsibly sourced and RDS certified and treated with the environmentally-friendly Ultra-Dry Down™ treatment.


All of which means you can rest easy.

Responsible Down Standard (RDS)

All Sea to Summit sleeping bags use only down which is certified according to the Responsible Down Standard. The RDS is helping shift the entire down and feather industry towards more humane animal rearing and handling practices. Overseen by the industry leading Textile Exchange, the RDS requires independent, third-party assessments of all aspects of animal rearing and handling throughout the entire supply chain. By using only down that meets the audited requirements of the RDS, we can have confidence that each phase of the collection process has been completed with the welfare and ethical treatment of waterfowl in mind.

To learn more about RDS, visit

Zip Coupling

Down and synthetic bags identified with our zip coupling symbol use a 65 inch #5 YKK full-length zip which allows a unisex left-handed and women's specific right-handed bag to pair together.

Designed to pair side by side, each person sleeps in their own bag enabling each of you to take advantage of your bag's unique insulation zones, hood and footbox features - perfect for cozy adventures for two.

Bags with full-length #5 YKK zips on both sides can also be coupled together with other pairing bags.

Free Flow Zip

Our Free-Flow triple-zip design ensures your sleeping bag retains maximum warmth and efficiency when needed and multiple ventilation options when it's not. 

The half-zip on the right side of the bag (left side on women's bags) provides freedom of movement for both arms, additional ventilation and allows the top third of the bag to be folded down as a mini quilt when the mercury climbs higher than expected.

Tech Specs

Product Details

Best Use
Comes With
Ultra-Sil™ compression bag and storage cell
Ultra-Dry Down 750+ Loft
Relaxed Mummy
Shell Fabric
Lightweight 20D Nylon Shell
Zip Options
Free-Flow zipper system
ascent-down-sleeping-bag-25-f-15-f-0-f-regular.svg ascent-down-sleeping-bag-25-f-15-f-0-f-long.svg
Ascent 1
1lb 14.3oz / 860g
4.9 L
S - 10L to 3.3L
11.6oz / 330g
6 ft / 183 cm
2.5 Season
25°F (Lower Limit)
35°F (Comfort Limit)
Ascent 1
2lbs 0.8oz / 930g
6.4 L
S - 10L to 3.3L
13.1oz / 370g
6 ft 6 in / 198 cm
2.5 Season
25°F (Lower Limit)
35°F (Comfort Limit)
Ascent 2
2lbs 6.8oz /1100g
6.2 L
S - 10L to 3.3L
19.4oz / 550g
6 ft / 183 cm
3 Season
15°F (Lower Limit)
27°F (Comfort Limit)
Ascent 2
2lbs 10.2oz / 1195g
7.8 L
M - 14L to 4.5L
21.7oz / 615g
6 ft 6 in / 198 cm
3 Season
15°F (Lower Limit)
27°F (Comfort Limit)
Ascent 3
2lbs 14.7oz / 1325g
8.2 L
M - 14L to 4.5L
26.5oz / 750g
6 ft / 183 cm
0°F (Lower Limit)
15°F (Comfort Limit)
Ascent 3
3lbs 3oz / 1445g
10.2 L
M - 14L to 4.5L
29.6oz / 840g
6 ft 4 in / 192 cm
0°F (Lower Limit)
15°F (Comfort Limit)
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