Thermarest Saros 0 Synthetic Sleeping Bag

-18°C Comfort Limit (EN13537:2012), 1875g of eraLoft Synthetic Insulation
Weighs 2232g (Regular bag)
Code: SS20535
  • £164.99
  • (FREE Delivery on orders over £15)
  • RRP £179.99
Item out of Stock | Usually dispatched within 24 hours

Thermarest's top-rated Saros Synthetic sleeping bag offers a warm, lightweight and fully-featured sleeping bag for cold weather comfort while camping and backpacking.

Thermarest says:

When the weather gets frigid and the forecast looks damp, the Saros 0F/-18C is equipped to keep you resting better. The Saros uses our eraLoft™ synthetic insulation, which is quick-drying and weather resistant, making it ideal for backpacking and mountaineering in wet weather from spring to fall. The fit of the bag has been perfected in our onsite cold chamber to create our W.A.R.M. fit that allows room for multiple sleep positions without compromising thermal efficiency. Our SynergyLink™ Connectors also integrate the Saros with your pad to ensure superior comfort with efficient warmth and the freedom to move as you like for the best night's rest possible. The Saros is offered in three sizes and designed to fit both men and women. Compression sack and storage sack included.

Therm-a-Rest's Saros range is designed to provide a rival the Questar down bag. If you prefer a synthetic bag that stays drier for longer and doesn't lose the ability to stay warm when wet then this is a great bag. In recent years advances in synthetic insulation have made it much lighter weight and smaller in terms of pack size. It is still heavier and larger when packed than a down bag but the benefits of synthetic can be worth it. This bag has an impressive Comfort Limit of -18°C so it is ideally suited to winter conditions across the UK.

The bag has been built with eroLoft insulation to keep you warm and dry during fast and light adventures. It's filled with a 65-35 distribution, placing more fill on the top and less on the bottom where the fill gets compressed. This saves weight and gives you a smaller pack size. The synthetic fibres repel water to keep you dry in damp conditions. Important in case you do get caught out.

It has all the usual features you'd expect from a quality sleeping bag including a draft collar, full-length zipper draft tube, snag-free zipper, cinchable hood and external zip pocket. There is also an extra foot pocket inside to provide a bit more comfort and warmth, particularly for anyone with cold toes. In addition to these there are also sleeping mat connectors on the back of the bag and loops on the front so you can add a quilt, both building on the versatility of the Thermarest sleep system concept. If you pair the bag with an insulated mat you will get a warmer bag for less weight.

- Reviewed by Ultralight Outdoor Gear

Read reviews here:

Help and advice: Choosing a sleeping bag advice
  EN 13537 rating for sleeping bags explained
  Sleeping bag shape and sizes advice
  Sleeping Bag features Page 1
  Sleepin bag features page 2
  • eraLoft™ Insulation: Efficient and compressible, our water-resistant synthetic fill uses hollow fibers to reduce weight without sacrificing warmth.
  • W.A.R.M. Fit: With Additional Room for Multiple positions (W.A.R.M.) fit means this bag allows for various natural sleep positions while maintaining thermal efficiency. 
  • SynergyLink™ Connectors: Integrate the bag with a pad for optimal comfort and thermal efficiency; removable for versatility.
  • Zoned Insulation: Maximizes warmth and saves weight by intentionally placing fill where you need it most. 
  • Toe-asis™ Foot Warmer Pocket: Ergonomic toe box that rapidly warms cold feet in a pocket of warm insulation. 
  • Quilt and Blanket Loops: Customize your sleep system by layering our quilts or tech blankets for increased warmth. 
  • Additional features: Heat-trapping draft collar, full-length zipper draft tube, snag-free zipper, cinchable hood and external zip pocket. 
  • Compression sack and storage sack included.

Temperature Rating

  • EN13537:2012 Comfort: -10°C / 14°F
  • EN13537:2012 Comfort Limit: -18°C / 0°F


  • Weight: 2232g (excludes bags)
  • Fits: 183cm / 6ft
  • Shoulder girth: 160cm / 63in
  • Hip girth: 155cm / 61in
  • Footbox girth: 117cm / 46in
  • Fill weight: 1875g
  • Packed dimensions: 28 x 30cm / 11 x 12in


  • Shell: 20D Polyester RipStop w/ DWR
  • Lining: 20D Polyester Taffeta
  • Insulation: eraLoft™ Polyester Hollow Fiber
Showing our 1 review for Thermarest Saros 0 Synthetic Sleeping Bag. Write a review ›
Review Summary - 5 out of 5 based on 1 rating.
April 18, 2021 | Tom Hughes
Thermarest saros 0°-18°

Great warm comfy bag. Thick insulation. Tested mine to -6° and it was absolutely toasty without liner or booties. Pack size is large, almost fills a 70L pack so unless your driving to camp it's not what we call a backpacking bag by a long shot. At 4lb it's a beast but it is really warm and snug. I slept really well for three nights, warmest was - 4° next to a lake.

Ultralight Outdoor Gear Limited