Let's go on an expedition: Therm-a-Rest Polar Ranger Sleeping Bag review

Therm-a-rest Polar Ranger Sleeping Bag review in a nutshell: If you need a sleeping bag that can keep you warm no matter the temperature outside, you'll need the Polar Ranger. Made from recycled and responsibly-sourced materials, Therm-a-rest's four-season sleeping bag is the ultimate cold-weather accessory for adventurers.

It's not often that I get to test four-seasons sleeping bags for our best sleeping bag guide in actual sub-zero conditions, but this is precisely what happened when I took Therm-a-rest's Polar Ranger on a trip to Mongolia. That adventure provided the perfect opportunity for me to test the capabilities of the Polar Ranger; one night, we even got to sleep on the ice.

Thermarest might be better known for being the manufacturer of the best camping mats (the Therm-a-rest NeoAir XLite Camping Mat I used is T3's top choice in the guide), but its sleeping bags are also gathering traction and for a good reason. Like their other products, Therm-a-rest sleeping bags are responsibly made, high-quality and durable products. In fact, the Polar Ranger is probably the first and last four-season sleeping bag you'll buy. Why? Read my full Therm-a-rest Polar Ranger Sleeping Bag review to find out.

Therm-a-rest Polar Ranger Sleeping Bag review: Price and availability

The Therm-a-rest Polar Ranger is available to buy now from third-party retailers such as Snow+Rock, GO Outdoors, Cotswold Outdoor, etc., for around £700 (approx. $865/AU$1,295). Therm-a-rest doesn't sell the Polar Ranger directly through their website; however, you can use their store locator to find the nearest shop that sells the sleeping bag. The company offers a Limited Lifetime Warranty on the Polar Ranger. To get your gear repaired, you must submit a warranty claim (more info can be found at Therm-a-rest). Compression sack and storage sack included in the price.

Therm-a-rest Polar Ranger Sleeping Bag review: Design and build quality

The Therm-a-rest Polar Ranger is an incredibly well-designed and sustainable sleeping bag. Its shell and liner are made from GRS-certified 100% recycled fabrics. The eco-friendly materials are lightweight, soft and durable, and filled with 800-Fill Nikwax Hydrophobic Down, which is PFC-free, absorbs 90% less water, and dries three times faster than untreated down. The down is also Responsible Down Standard Certified.

One of my favourite features is the Snorkel Hood (or, as my fiancee likes to call it, the Blow Hole); it's designed to allow for easy breathing and ventilate exhaled moisture to preserve loft. In my experience, the small breathing hole also helps keep external sound levels to a minimum. The Snorkel Hood has a magnetic closure allowing easier entry and exit.

Another cool feature is the Side Vent, or more like the Side Vents, as there are two. These zipped holes can help regulate the temperature in the sleeping bag better – I used them to create a little draft inside – and allow you to use your hands outside the sleeping bag while keeping your core warm. For example, you can use your smartphone or read a book without leaving the toasty comfort of your Polar Ranger. The Side Vents have overlapping draft tubes to prevent cold spots when closed.

There is a zipped pocket inside to keep your valuables, phone, etc., close to you. The pocket is also helpful for keeping your most important gear above sub-zero temperatures. At the back, you'll find two SynergyLink Connectors that secure the bag to your sleeping pad.

I saved the best feature last: the Toe-asis Foot Warmer Pocket. This area of the sleeping bag doubles down on warmth, making it all the easier to feel warm in the Polar Ranger. That said, the overstuffed draft tubes, external quilt loops, and draft collar generally makes being in the Therm-a-rest Polar Ranger an extra cosy experience.

Therm-a-rest Polar Ranger Sleeping Bag review: Performance and comfort

The Therm-a-Rest Polar Ranger has a comfort rating of -20°C/-4°F and a limit of -30°C/-20°F. This means even if you're a cold person, you should feel considerably warm in the bag, even if it's -20°C outside. I'm not a cold person, and the Mongolian ger I slept in had a little wood burner stove in the middle to provide some warmth, but I never for a moment felt cold in the Polar Ranger.

If anything, I had to use the Side Vents and allow some air inside the bag to keep me from overheating (I'd like to pressure that I walk around in my underwear at home, even in the middle of winter). I appreciated that I could easily manage the temperature inside the sleeping bag using the main YKK zipper and the Side Vents.

The Polar Ranger has an oversized design, meaning you can wear your down jacket, walking trousers and even your hiking boots while in the bag, should you feel the need for some extra layers. I tried it while wearing my The North Face Nuptse jacket and boots, and the Polar Ranger wasn't even remotely snug. I usually slept in only base layers, even when the temperature hit -22°C outside the ger one morning.

This doesn't mean I let the extra space inside the bag go to waste. No, I usually kept extra hiking socks and base layers I wanted to use the day after in the Polar Ranger to ensure they were warm enough to put on. I kept my phone in the internal pocket for the same reason (and inside my down jacket when I was trekking on the ice).

The Threm-a-Rest Polar Ranger struggles a bit with packability. I tested the long version, which weighs a hefty one and a half kilos (3 lbs 7 oz). The bag comes with compression and storage sacks; trying to get the Polar Ranger into the former is challenging due to the sheer size of the bag. It's not impossible, and once you've done it a few times, it'll be much easier, but I spent around half an hour trying to compress and push it into the little sacks the first time.

The storage sack is more accommodating but also huge, so if you're backpacking, you'll need to use the stuff sack. A little sacrifice to make, considering the temperature rating of the Polar Ranger (if you ask me). 

Therm-a-Rest Polar Ranger Sleeping Bag review: Verdict

The Therm-a-Rest Polar Ranger is the ultimate cold-weather sleeping bag. It's warm, extremely comfortable, sustainably made, and just a fantastic piece of outdoor equipment overall. The 800-fill Nikwax Hydrophobic Down filling is durable and made with Responsible Down Standard Certified down; it'll keep you toasty even in the coldest temperatures.

Should you feel warm, you can always open the Side Vents to control the temperature inside the Polar Ranger. However, you'll likely need to stay warm, and the overstuffed draft tubes, external quilt loops, and draft collar ensure the heat won't escape from inside the bag. Not to mention, thanks to the Toe-asis Foot Warmer Pocket, your feet will always feel cosy, making it almost impossible for you to feel cold.

The only criticism I can offer is the size and weight of the Polar Ranger. Still, I know it would be unfair to expect something that can keep you warm in extreme temperatures and be super lightweight and packable (plus, if it were, we might have to add it to our best lightweight sleeping bag guide, which wouldn't be fair with other bag manufacturers). That said, you can compress the Polar Ranger down to a compact size (with some effort), so even if you're backpacking, you can easily carry it with you. Highly recommended!

Therm-a-Rest Polar Ranger Sleeping Bag review: Also consider

If you need something less extreme, the Rab Neutrino 400 Sleeping Bag might be your best option. With a temperature limit of -7°C / 20°F, the Neutrino 400 is designed to offer a balance of warmth and lightweight, intended for mountaineers and alpinists. Read Mark's full Rab Neutrino 400 Sleeping Bag review.

The Kelty Cosmic Ultra 20 Sleeping Bag is ideal for adventures in most weather conditions, with sizes to fit most campers and offering impressive value for money, too. Weighing a little less than the Polar Ranger, the Cosmic Ultra 20 is perfect for weekends outdoors or more casual wild camping, as well as for traditional camping trips. Read Sian's full Kelty Cosmic Ultra 20 Sleeping Bag review.