Warming for girls. Sea to Summit Thermolite Reactor Compact Plus Liner.

Why are there inserts at all? One of the important functions of the liner is to extend the life of your sleeping bag. After all, it is not often possible after a camping day to organize water treatments and climb into the bedroom clean and fresh. Therefore, the derived “bed” is contaminated. Each wash of the sleeping bag has a negative effect on its filler, which makes it worse and worse insulates. And washing a sleeping bag is not the easiest fun. At the same time, the liner can be easily machine washed at least after each trip without compromising its thermal insulation properties. And replacing a liner, even if it fails, is much cheaper than replacing your favourite sleeping bag.

Inserts are often bought for insulation. In combination with the sleeping bag, the liner forms an additional layer of air near the body, thus creating another barrier to heat, which is so eager to escape from you into the environment. The thicker the liner and the better the insulation of its materials, the more degrees you can “subtract” from the comfort temperature of your sleeping bag.

In addition, the liner is hygiene. If you rent a sleeping bag or borrow from friends, the liner will not only be a cozy and part of your camp bed, but also a guarantee of your cleanliness. In addition, it can be used instead of bed linen in trains, hostels and overnight Couchsurfing.

A year ago, I looked in the direction of the liners in search of extra warmth for my sleeping bag. It was a much cheaper and easier way to achieve the right insulation than buying a new sleeping bag with a comfortable temperature a few degrees lower. You could sleep in clothes, but it was a hike through warm Turkey and in the morning after a cold night it warmed up very quickly. In the case of clothes, I would have to get up and undress every morning to sleep for another hour or two after the sun rose. And with the liner, it was enough to unzip the zipper in the middle of the night and throw the top of the sleeping bag aside.

Fleece and thermolight inserts perform the best insulation mission. As the first is quite heavy and bulky, I looked to the second option.

Thermolite is a hollow fibre material that has good thermal insulation properties at low weight. In it, the air is retained not only in the layer between the threads but also inside the fibres themselves. Namely, the immobilized air protects well from the cold.

Sea To Summit has a line of Thermolite inserts under the general name “Reactor”. Its advantage is also that the fabric in these inserts is made by the technology of knitting, and not the usual weaving. As a result, the product becomes more elastic and stretches much better. This means that you can move inside the liner as you wish without feeling pressure from all sides. This is especially noticeable if in the summer on warmer nights you sleep in the liner, without a sleeping bag.

In addition, Thermolite is synthetic, so the material will cope better with the removal of moisture and will warm better when wet. For example, after unpacking things in the rain, getting condensate on the liner or just sweat.

The Reactor series has four liners, each of which is made of thermolight of different specific gravity. Accordingly, each liner will provide a different level of thermal insulation. For example, Thermolite Reactor, at its own weight of 248 grams, should improve the comfort temperature of your sleeping bag to 8 degrees. Women’s Thermolite Reactor Compact Plus – up to 11 degrees at a weight of 263 grams. Thermolite Reactor Extreme – up to 15 at 399 grams. And Thermolite Reactor Fleece Liner – up to 18 degrees at a weight of 420 grams.

The hero of today’s review, Thermolite Reactor Compact Plus, for me is the most successful compromise between the extra heat and the extra weight that will have to carry in a backpack.

In addition, its volume in the uncompressed state is very small: a little less than a litre bottle of Hydrapak Stash. And, if desired, it can be compressed by another third.

The features of this model are the zoning of materials and the shortened size. The main material is the thinnest Thermolite available today, weighing 80g / m2. In the areas of the greatest heat loss – on the torso and in the football – a thicker Thermolite 110g / m2 was used. To visually remind consumers about zoning, the manufacturer has used different colours for different fabrics: thicker Thermolite red, thinner – black.

The total length of the liner is 183 cm. In our experience, it is suitable for travellers up to 170 cm. And although the manufacturer calls it “compact” and not “feminine”, I had to use the last word in the title to draw your attention to its unique size. After all, almost 100% of negative reviews about this liner are “It’s kind of short.” Yes, it is shorter than the others, but this is done specifically with care for those short tourists who do not want to wear extra fabric on their backs just because the manufacturer has unified the size, making one for everyone. And Sea To Summit warns everyone about the size of the liner. But few people read those small letters on the package. And in vain 🙂

Thermolite Reactor Compact Plus shape – cocoon. This means that it will be perfectly combined with a sleeping bag of a similar shape and will not take up too much space inside.

At the same time, his football has an anatomical shape, which also adds comfort during sleep.

The hood of the liner is flat and wide, unfolds completely.

But it can be tightened around the head with a cord with a small clamp.

The liner is packed in an ultralight bag made of reinforced siliconized nylon, with a thread thickness of 30D. Rip-stop weaving adds strength to the fabric and, in the event of a puncture, prevents the gap from widening.

The ends of the bag are made of thicker reinforced nylon, about 70D. Thanks to the inscription on the lower end, the liner can be easily found on the shelf with other equipment.

The entrance of the bag is tightened with a thin cord and a miniature clamp (identical to those in the hood). For some reason, the end of the cord is sewn into the base of the bag. It would be much more convenient to work with free.

Also on the bag is sewn 20mm sling to manipulate it. However, for this purpose, I prefer the handle or a sling on the end face opposite from an entrance.

Own experience

Of course, the manufacturer quite cunningly approached the heat characteristics of the Sea To Summit Thermolite Reactor Compact Plus liner. The bright inscription “adds up to 11 degrees” is perceived by our mind on the positive side and we mentally subtract the specified number from the comfort temperature of our sleeping bag. But for some reason, we don’t notice the small “to”. Although, 2 is also within “up to 11” 🙂

The fact is that the liners can not write something specific. Because there is no standard for them. And all the tourists and the conditions in which they fall are so different that no one is able to prescribe all possible cases. In addition, lowering the comfort temperature from +15 to +10 is not the same as from -10 to -15, although the arithmetic difference in degrees will be the same. That’s why manufacturers write something to give a starting point, but in fact, it all depends on many factors.

From my own experience, I can say that for the summer season you can focus on 4-6 additional degrees of comfort. That is, I redesigned my SeaToSummit Spark SpI with a female comfort temperature of +12 with the help of the Sea To Summit Thermolite Reactor Compact Plus into a system that retained my heat well at a temperature of + 6… + 8. In the winter, in my opinion, about 2-3 additional degrees were added to the sleeping bag.

The second thing I want to say – the material and comfort of sleep. I was very worried that I would get entangled in the liner during sleep because I was spinning a lot. In fact, this was only the first time. Perhaps in all the following, I was already accustomed to feeling an extra layer of fabric inside the sleeping bag. The material itself is very tactile, so inside the liner, especially on hot days, sleep is much more comfortable than on bare nylon sleeping bag.

What turned out to be unexpected for me is that the red zones really add more warmth. To me, as a side-sleeper, that is, a person who mostly sleeps on his side, it became noticeable on the first night when I felt that my back was colder than in front. Because returning to the side, I returned the liner with me. Thus, its red (warmer) area remained on the chest, and the back was covered only with black (thinner) material.

Later, when I fell asleep, I turned the liner over so that the red areas covered those parts of the body that needed more heat. Due to the large width of the liner (86 cm at the top) this can be easily done.

The Reactor Compact Plus, like the other Sea to Summit liners, has no zip. Only a huge neck, through which, in fact, you need to climb into the liner.

This design is a great way to save weight. But when a sleepy night needs to get out of the liner and sleeping bag, the lack of zipper is not very happy.

By the way, the best way for me was to get into the liner first, and only then into the sleeping bag. I did not succeed in the version “you put it in the sleeping bag, climb into both at once”.

As for the length, I would like to emphasize once again that the Reactor Compact Plus is quite short. After all, on American sites, I met a lot of complaints that someone bought the liner, and did not even hold it to his shoulders, although no one is to blame that people are lazy to read the description of the product before buying it.

An important plus – hygiene. It’s not just that now you can wash the liner at least after each hike and always sleep fresh and clean during the hike. For example, I use it on trains, because often the linen they give there can be damp, dirty and not very attractive for sleeping. Plus, as our co-author, Marina Sukhomlinova, said in her article when spending the night on Couchsurfing, hosts do not always consider it necessary to give guests bed linen. So here again, small liners come in handy.

And the last – multifunctionality. In addition to its primary functions – such as additional insulation and protection of the sleeping bag from dirt, I found in it a few other useful benefits for myself. For example, on very, very warm nights, it is more comfortable to sleep in it than in any bedroom. Even if you just cover yourself with a sleeping bag. After all, no matter how cool, the liner fabric is much nicer to the touch. However, in windy weather, it is better to sleep in a tent in a liner, rather than just in the open air or awning, because its material is easily blown away.

In addition, the liners are great to combine with quilts – in this case, you will gain less weight, because you use a quilt, not a sleeping bag, extra warmth, thanks to the combination of both products, and comfortable sleep, because you will not touch the body to the mat material.

Conclusions. Putting in a sleeping bag is not the most necessary thing in the traveller’s arsenal. And before you buy, you should think carefully about whether the liner is designed to solve the problem before you.

The liner protects your sleeping bag well from dirt, which is especially true for down products that should be washed as rarely as possible. It is convenient to take it on trips, where various temperature fluctuations are expected, and it is not an option to take an extra sleeping bag due to weight or volume. Or in those trips where the condition and cleanliness of beds are unknown (rent of sleeping bags, the railway, a couch, hotels in separate countries). In addition, it is more pleasant to sleep in a liner than just in a sleeping bag or a quilt. And, in the end, buying a liner is more often a budget decision than buying a new sleeping bag for a slightly cooler temperature.

At the same time, the material for the liner can be chosen depending on the needs – silk, if you just want protection from dirt and minimal weight, cotton, if you want to find a comfortable and budget option (however, remember that cotton actively absorbs water and is very lazy gives it away, dries for a long time), fleece – if you first need to keep warm, and weight and volume are not so important. And thermolight is a kind of compromise between all three options.


  • additional heat due to lightweight
  • additional hygiene
  • compactness, combination and zoning of materials
  • hood, foot place
  • multifunctionality
  • protection of a sleeping bag from pollution
  • the thought-over cover.

Disadvantages: no zipper.

Feature: shortened size for travellers up to 170 cm.

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