Therm-a-Rest Sleep Liner review: great performance in cool weather and multiple sizes

A warm and versatile all-rounder, the Therm-a-Rest Sleep Liner is available in three sizes

Therm-a-Rest Sleep Liner
(Image: © Therm-A-Rest)

Advnture Verdict

Great soft comfort, some added warmth and the chance to pick from three sizes make this Therm-a-Rest liner a good choice for cool weather, especially if you need a shorter or taller liner than most brands offer.


  • +

    Noticeably warm

  • +

    Good zip

  • +

    Brushed material


  • -

    On the slim side

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Therm-a-Rest Sleep Liner: first impressions

The Therm-a-Rest Sleep Liner comes in three different sizes: Small, Regular and Large. The Small (168cm) is a good pick if you own a female-specific sleeping bag and find that regular sleep liners are too long and tend to bunch up, while the Long is 198cm in length, so it’s ideal for taller campers. Even if you aren’t especially tall, we’d recommend picking the Long if you have wider shoulders, as you may find the Small and Medium offer too narrow and claustrophobic a fit.

But how did the Therm-a-Rest Sleep Liner perform under test conditions for our best sleeping bag liner buying guide? Read on…


• RRP: $44.95 (US) / £54.99 (UK)
• Weight: 320g / 11oz
• Pack size: 23cm x 12cm / 9in x 5in
• Material: Polyester
• Shape: Mummy
• Color: Grey
• Compatibility: Welcome warmth for slimmer campers on cool nights

Therm-a-Rest Sleep Liner: in the field

If you’re shopping for your first sleeping liner for cool nights, you won’t go wrong with Therm-a-Rest’s Sleep Liner. This well-made all-rounder ticked all our boxes on test – it adds warmth, it’s easily machine-washable and it has a good three-quarter zip to make getting in and out of the bag quick and easy come bedtime (no ungainly wriggling in and out of a tube of material here). 

Therm-a-Rest reckon their design adds three degrees of warmth, and we did find it noticeably trapped in more heat than using your best sleeping bag alone. We liked adding it to our sleep system (along with an insulating sleeping pad) on crisp, chilly nights, but reckon you’d overheat fast on hot summer nights unless you used the liner alone and partially unzipped it. 

While this bag is made with polyester, it’s got a brushed finish to the material that feels soft and not plastic-y to touch.

Sian Lewis

An award-winning travel and outdoors journalist, presenter and blogger, Sian regularly writes for The Independent, Evening Standard, BBC Countryfile, Coast, Outdoor Enthusiast and Sunday Times Travel. Life as a hiking, camping, wild-swimming adventure-writer has taken her around the world, exploring Bolivian jungles, kayaking in Greenland, diving with turtles in Australia, climbing mountains in Africa and, in Thailand, learning the hard way that peeing on a jellyfish sting doesn’t help. Her blog,, champions accessible adventures.