A liner keeps your sleeping bag clean, but a good one also makes it warmer. We took four Sea to Summit liners on our big trip from Sydney to Adelaide, Melbourne and back, and tried them all. The Sea to Summit Reactor Fleece Liner is our favourite: it’s the warmest of the four, and on milder nights it can almost work as a summer sleeping bag on its own. It cost us $110.
What’s in the box
A mummy-shaped liner made of soft grid fleece, 60% Thermolite EcoMade and 40% polyester, with a side zip, a hood that closes with a drawcord and a shaped footbox. It comes in a grey stuff sack with a drawcord, and the fabric has HeiQ Fresh odour control. On the box Sea to Summit rates its warmth boost as “Blazing”, the top of its scale.
What we like
- Adds up to 8°C of warmth
- Almost a summer bag on its own
- Side zip: easy in and out
- Drawcord hood and footbox
- Soft, warm grid fleece
- HeiQ Fresh odour control
What we don’t
- Heaviest of our four: 379 g
- Biggest packed: 20 × 13 × 13 cm
- Snug mummy shape
Quick Specs
| Spec | Details |
|---|---|
| Brand | Sea to Summit |
| Material | 60% Thermolite EcoMade40% polyester grid fleece |
| Weight | 379 g |
| Packed size | 20 × 13 × 13 cm |
| Shape | Mummy |
| Temperature rating | Adds up to 8°C |
| Features | Side zipDrawcord hoodFootboxHeiQ Fresh odour control |
Warmth
This is why it’s our favourite. The grid fleece is thick and soft, and Sea to Summit says it adds up to 8°C to your sleeping bag, more than any of its other Reactor liners. Inside a three-season bag it takes the edge off cold nights, and on milder nights in the rooftop tent it almost works as a summer sleeping bag on its own.
Side zip and hood
Unlike the other Reactor liners, the Fleece has a zip down the side, so you don’t have to wriggle in from the top. A snap at the top of the zip keeps it closed, and the hood pulls in around your head with a drawcord. The trim around the opening is a darker grey, which makes it easy to find the hood in the dark.
Shape and size
It’s a mummy shape, wide at the shoulders and narrower towards the feet. The foot end is open, with a drawcord around it: pull it tight and it closes into a rounded footbox, so the liner follows the inside of a mummy or tapered sleeping bag without bunching up. That also means it’s snug: if you like room to move, the rectangular Comfort Blend is roomier.
Weight and packing
The warmth comes at a cost: at 379 g it’s the heaviest of the four, and it packs to about 20 × 13 × 13 cm, the biggest of the lot. For car camping and touring that doesn’t matter much, but for hiking the lighter Reactors make more sense. If you only want a liner to add warmth for car camping, the Coleman Stratus Fleece Liner is a cheaper, heavier option.
Vs the other liners
We’ve reviewed all four Sea to Summit liners we took on the trip. The Reactor Extreme and Reactor Lightweight are made of a stretchy Thermolite Pro knit and add less warmth, but pack smaller, and the Comfort Blend is a rectangular liner made to keep you cool.
This review Reactor Fleece |  Comfort Blend |  Reactor Extreme |  Reactor Lightweight | |
|---|---|---|---|---|
| Adds warmth | 8°C | – | 6°C | 4°C |
| Material | Grid fleece | Coolmax, Tencel | Thermolite Pro | Thermolite Pro |
| Shape | Mummy | Rectangular | Mummy | Mummy |
| Opening | Side zip | Top, no zip | Top, snaps | Top, snaps |
| Packed size | 20 × 13 × 13 cm | 15 × 7.5 × 12 cm | 19 × 11.5 × 11.5 cm | 18 × 10 × 10 cm |
| Weight | 379 g | 290 g | 350 g | 286 g |
| Price paid | $110 | $60 | $130 | $90 |
| Our score | 9.3 | 8.5 | 8.9 | 8.7 |
Conclusion: Sea to Summit Reactor Fleece LinerConclusion
The Sea to Summit Reactor Fleece Liner is the warmest liner we’ve used: a soft grid fleece mummy liner that adds up to 8°C, with a side zip, a drawcord hood and a shaped footbox. On milder nights it almost works as a summer sleeping bag on its own. It’s the heaviest and bulkiest of the four at 379 g, but for $110 it’s our favourite, and the one we’d pick for car camping and touring.
A grid fleece mummy liner that adds up to 8°C and almost works as a summer bag on its own, with a side zip and drawcord hood.
Heavier and bulkier than the other Reactors.
- Car campers
- Rooftop tents
- 4WD tourers
Yes. For $110 it makes a three-season sleeping bag noticeably warmer, and on mild nights you can leave the bag in the car. If you want to save weight, the Reactor Extreme or Lightweight pack smaller.
