When we set out developing the Saros™ sleeping bag we aimed to boost our Trek & Travel series with the best synthetic sleeping bag possible. Our Trek & Travel category is about versatility, and the Saros embodies the category. The Saros is an excellent choice for the everyday adventurer who wants to access the backcountry one week and car camp with family and friends the next. Most of all, the Saros is great if you do all that in the wet and stormy conditions that keep others inside.

saros best synthetic sleeping bag models

Saros Sleeping Bag Models

The Saros is available in three different models. Each filled with a precise amount of eraLoft™ Insulation to fit three temperature ranges. Naturally, the winter-ready Saros 0F/-18C is the heaviest, followed by the versatile Saros 20F/16C, with the Saros 32F/0C weighing the least. Check the weight breakdown of each model below (reg size):

Weight and Temperature

  • Saros 0F/-18C: 4lb 15oz (2235g)
  • Saros 20F/-6C: 3lb 3oz (1457g)
  • Saros 32F/0C: 2lb 130z (1272g)

Temperature ratings are trickier than many people realize. In a perfect world, the variables held constant in the EN/ISO test would be held constant out in the field, and sleepers could absolutely stake their overnight warmth in the rating of their bag. But reality’s imperfections are what make it interesting. Factors such as what and when a sleeper eats, humidity, and what is in the rest of the sleep system are just three things that effect a sleeper’s temperature.

A critical factor, however, is sleeping bag fit. A properly fitted sleeping bag should correspond with your height as much as possible. If your bag is too long energy that should be heating the space around your body heats up empty space instead. This was a major reason why we did away with distinct Men’s and Women’s models, and now make unisex sleeping bags, the Saros included. The more universal size options of unisex designs provided all of our customers with easier access to a bag that fit them properly.

Even with a dialed fit, real world variables can make it difficult to predict a warm night or a cold one. Which is why the Saros bags, like all Therm-a-Rest mummy bags, utilize the EN/ISO temperature range scale to better inform users.


Unlike warmth-to-weight, there’s no measurable “performance-to-price” metric, but that doesn’t stop everybody from thinking in those terms. One of the best things about the Saros sleeping bag is what you get for what you pay.

The MSRP price breakdown for each bag is listed below (reg size):

  • Saros 0F/-18C $199.95
  • Saros 20F/16C $179.95
  • Saros 32F/0C $159.95

The Saros is an ideal bag for newcomers on account of the price point, yes, but there is more to it than that. A well thought out feature set offers a refreshingly useful user experience with design elements that actually make a difference. In fact, the Saros offers all of the same features as our popular Questar series, but in a Synthetic design. Made with high quality materials and the legendary craftsmanship that Therm-a-Rest is known for, both new campers and veterans stand to gain a durable piece of gear they can rely on for years.

saros sleeping bag

Saros Design and Features

The Saros manages to be feature rich without excess. It’s loaded with clever design elements that make sense together and combine for a class leading user experience. We believe this is a mark of the what the best synthetic sleeping bag should be.

W.A.R.M. Fit

The Saros bag is intended to be versatile. That means excelling out on the trail in the backcountry as well as on a weekender car camping trip. To accomplish this, we had to make the bag light, packable and super comfortable.

The comfort is brought to you by W.A.R.M. Fit, which stands for With Additional Room for Multiple Positions. The industry calls them mummy bags, but few people actually sleep like a mummy. In a lot of backcountry-going sleeping bags, side sleepers and active snoozers can be a bit out of luck in terms of comfort.

W.A.R.M. is a roomier cut to accommodate real human sleep positions. The internal measurements of a regular size Saros is 63 in (160 cm) through the shoulder, 61 in (155 cm) in the hip and 46 in (117 cm) in the foot box. Put another way, you can change your underwear in the sleeping bag without issue.

Importantly, W.A.R.M. Fit creates room without losing thermal efficiency. Many “wide fit” bags on the market have lots of excess, unusable space. This space causes these bags to be heavier, less packable, more expensive, and most importantly, less warm. Decades of expertise in comfortable outdoor sleep allowed us to accurately provide room where its needed and cut it back where its not. Combined with the innovation of Zoned Insulation, the Saros provides roomy comfort and easy warmth.

stargazer_regular_draft sleeping bag

Zoned Insulation

The thermal efficiency achieved by W.A.R.M. Fit is made possible by Zoned Insulation. Zoned Insulation is our technique of accurately prioritizing certain areas in the sleeping bag that need insulation, and uncovering the areas that need less.

Most significantly, we reduce the amount of insulation in the bottom of the Saros. By doing so, the overall weight of the Saros decreases, it’s packed size shrinks, and more eraLoft™ insulation can be placed where it is more useful. Where is it more useful? On the top of the bag through the torso where the extra room of W.A.R.M. Fit can then be properly heated.

But what about the bottom, how is it properly heated? The answer is R-Value. R-Value is the measure of the insulation your sleeping pad provides from the cold ground. Assuming it has the appropriate R-Value, your pad is much better at insulating than the bottom of your sleeping bag.

Insulation, whether it’s down or synthetic, needs loft to create the pockets of heated air that keep you warm. The insulation on the bottom of any sleeping bag becomes compressed and can’t create an effective amount of air pockets.

Using SynergyLink™ Connectors, the Saros attaches to your sleeping pad to ensure that the sleeper is insulated from the bottom throughout the night. Even if you roll from side to side, you won’t expose the bottom of the sleeping bag and lose heat.


The Saros is a bag designed to integrate with a pad, rather than just lay on top of it. Selecting the right pad for your sleep system is very important. Many pads will do the job, but the Trail Pro™ matches the Saros in terms of outsized comfort and versatility with an R-Value suitable for year-round adventures.

Other Features

Similar to the SynergyLink Connectors, the Saros has other elements that contribute to its excellent user experience. The heat-trapping draft collar and full-length zipper draft tube minimize heat loss and boost luxurious comfort. The snag-free zipper prevents frustrating tears and makes ventilation adjustments from inside the bags a breeze. Meanwhile, an external storage pocket keeps essentials within reach at all times during the night.

Yet the feature that is most popular with Saros users might just be the Toe-Asis™ Foot Warmer Pocket. Tucked into the footbox of the bag, this pocket rapidly warms toes and makes carrying sleep socks unnecessary—though an extra pair of socks is always recommended.

The Synthetic Difference

Synthetic insulation is all about versatility. Though down insulation is superior in its warmth-to-weight ratio, it still can’t match the performance of synthetic insulation when it is wet,  despite the advent of DWR treated down. Synthetic insulation is also cheaper. Investing in the Saros is a great way to get high, versatile performance without breaking the bank.

eraLoft™ Insulation

Therm-a-Rest’s proprietary synthetic insulation, eraLoft, delivers impressive temperature regulation with the use of hollow fibers. The hollow fibers boost heat while still being remarkably compressible and water resistant. It has also been commended over the years for its durability, being used by various guide services and outdoor educational institutions.

synthetic sleeping bag with era loft

Who is the Saros For?

At its price, the Saros automatically becomes one of the best synthetic sleeping bag choices for a first-time sleeping bag buyer. But it’s about more than just price. New campers acquiring gear should look for gear that is made well, durable and able to perform as they dive deeper and explore new forms of outdoor adventure.

By staying light, being packable and excelling at overcoming wet weather the Saros checks these boxes. Ultimately, those advantages of the Saros make it a great bag for experienced adventurers as well. With experience, one eventually realizes that nature has a way of delivering the unexpected. Being prepared is critical and the Saros ensures that comfortable sleep is always an option.

Final Thoughts

Part of our job entails thinking about the people out there that took the leap, went into the outdoors for the first time, had a bad experience and never came back. We wonder if they had used different gear—the right gear—if the outcome would have been the same.

As experienced backpackers and campers, we at Therm-a-Rest would have some choice gear recommendations for many of those people. We keep using and loving our Saros bags, and would certainly tell any new comer to not hesitate to be prepared, and pick up one of the best synthetic sleeping bags on the market. To pick up a Saros.