• Length (standard) 210 cm
  • Width (standard) 90 cm
  • Weight 399 grams
  • Cost $111.99

Sea to Summit THERMOLITE Reactor Extreme Liner

Sleep Systems


Rating: 9 / 10
Durability 1.8 / 2
Value for Money 1.8 / 2
Warmth 1.9 / 2
Weight 1.7 / 2
Versatility 1.8 / 2

Sea to Summit THERMOLITE Reactor Extreme Liner Review

Comfort has a big impact on whether we get a good night sleep when on a hiking trip. For each of us there is a list of things that will enhance or detract from our perception of comfort. For me the factors include being warm but not too warm (or too cool), the ability to roll over easily (without getting wrapped in my sleeping bag), being ‘covered’ and having a clean place to lay my head.

Those of you who don’t use a sleeping bag liner should think deeply about that last point. Your sleeping bag does get dirty and it is a complex exercise to clean your sleeping bag and for its durability, you shouldn’t wash it too often! So the best way to protect your treasured sleeping bag is to use a sleeping bag liner.

We have previously reviewed the Sea to Summit 100% Silk Travel Liner but for some reason we hadn’t got around to reviewing the Sea to Summit THERMOLITE® Reactor Extreme Liner. I have been using the Reactor Extreme Liner for so long now I can’t even remember how long. I recall I purchased my Reactor Extreme Liner in 2012 when we were heading off to do the Bhutan High Trails. Despite that being quite a few years back it is still going strong with no sign of wear.

The great thing about the Reactor Extreme is that it will give you a greater range of temperatures across which your sleeping bag will be effective. In fact, the Reactor Extreme Liner will add up to 15° Celsius to the comfort rating of your sleeping bag. So if you only occasionally do overnight hikes in cool temperatures then you can supplement your existing sleeping bag to cover the difference. This means that in addition to extending the life of your sleeping bag by keeping it clean, you’re also extending its performance range.

The Reactor Extreme Liner is roomy despite having a slight tapering from head to toe. It has a top drawcord which enables you to reduce airflow further and snuggle in for extra warmth. It is made from a stretch fabric which means restless sleepers won’t feel ‘trapped’. The standard size is a generous 210 cm in length which suits even the tallest people comfortably. There is also a long version at 235 cm for the super tall. It comes in a bright tangerine colour so you won’t misplace it in a hurry. And it washes well without fuss and dries quickly in the sun or the drier.

During a few very cold nights on the Hume and Hovell Track, Tim took possession of my Reactor Extreme Liner to add some extra warmth to his 2° Celsius Sea to Summit Micro II Sleeping Bag and it worked a treat! He couldn’t believe how much warmer he was.  Of course, from then on the challenge was to wrestle my Reactor Extreme away from him!

When I don’t need the Reactor Extreme Liner for warmth, I usually have it over my Therm-a-rest NeoAir XLite Women’s Sleeping Mat to stop it slipping around during the night (and to dampen the noise a little).

This liner is at the dearer end of the range at just on AUD $112 RRP but for the extra warmth it creates you will really appreciative this if you are a cold sleeper.

The Sea to Summit THERMOLITE® Reactor Extreme Liner is without doubt the most value for money hiking kit in which I have invested – it is durable, has many uses and is super warm! This liner is always at the top of my sleep system considerations when packing for a hike (Gill).

We Like

  • Super extra warmth by up to 15º Celcius
  • Tapered with a box foot so you won’t feel trapped
  • Drawcord hood with mini cord lock that lets you snuggle down
  • It is very durable
  • A great way to keep your sleeping bag clean and extend its life

We Don't Like

  • At a touch under 400 grams it is a bit on heavy side

Best Uses

  • Ideal for use on its own or as a sleeping bag liner that extends your bag warmth
  • Extends the life of your sleeping bag by keeping it clean

Buy One

You can purchase Sea to Summit THERMOLITE Reactor Extreme Liner online from Snowys, Wild Earth, or from Wildfire Sports

Disclosure:  We may earn a small commission, at no additional expense to you, if you click through and make a purchase. Please note that our affiliations do not influence, in any way, the independence of our reviews. If we don’t like a product, you’ll hear about it from us!


AUD $111.99 AUD but they always seem to be on sale somewhere!


Other Versions

Sea to Summit THERMOLITE Reactor Liners are available in the following versions:

  • Extreme
  • Reactor
  • Mummy
  • Fleece Mummy
  • Plus (compact) Mummy

Sea to Summit THERMOLITE Reactor Extreme Liner

Sea to Summit THERMOLITE Reactor Extreme Liner temperature rating


This review was done with product purchased from a retail store by Australian Hiker

Last updated

7 April 2024

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