Reviews / Sleeping

Sea to Summit Reactor Extreme Liner Review (2026)

Sea to Summit Reactor Extreme uses a merino/Thermolite blend rated to add 22°F warmth to any sleeping bag it's used inside. At 9 oz, it's the lightest 22°F supplement available — extending a 30°F bag to 8°F for unexpected cold snaps.

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Sea to Summit Reactor Extreme Liner — Sleeping review photo
Illustrative
9
Grant's score
The short version

Sea to Summit Reactor Extreme is the sleeping bag liner for extending bag temperature ratings in emergency cold conditions. We researched the 22°F warmth addition claim.

Who it's for

Buy this if: Backpackers who want one-bag versatility — a 30°F bag + Reactor Extreme covers 0-80°F with the liner in or out.

Skip this if: Hikers who never experience unexpected cold snaps — the liner adds 9 oz without benefit in predictable conditions.

In practice

One-Bag System Value

Carrying a 30°F bag + Reactor Extreme provides temperature coverage from 0°F to 80°F in a two-piece system weighing 25 oz (16 oz bag + 9 oz liner). A dedicated 0°F bag covers this range in one piece but weighs 36+ oz. The two-piece system saves 11 oz while providing the same cold-weather coverage.

What we loved
+ 22°F addition extends bag coverage significantly for 9 oz+ Merino component adds odor resistance for multi-day use without washing+ Doubles as a standalone sheet in warm hostels or hut sleeping
What we'd change
– $80-100 for a liner that covers gap scenarios only– Merino/Thermolite is hand-wash recommended
Where to buy

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Links are Amazon affiliate links — we earn a commission if you buy, at no extra cost to you. It never changes our score.

The verdict
9

The correct temperature extension tool for one-bag versatility. Not needed if you accept the temperature limitation of your single bag.

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Common questions

Can I use it alone?
The Extreme liner alone is rated to 68°F — works as a summer sleeping bag in warm conditions.
Does it fit inside any bag?
Designed for mummy bags. Works in rectangular car camping bags. Check dimensions if your bag is unusually narrow.

Methodology: Our gear ratings combine manufacturer specifications with aggregated owner feedback and long-term durability reports from verified buyers. We weigh value, packability, durability, and real-world reliability. Ratings are never influenced by commission rates. Last verified 2026-07-03.

Affiliate disclosure: This review contains Amazon affiliate links. If you buy through them, Gear Made Simple earns a small commission at no extra cost to you.

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