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Sea to Summit Reactor Plus Thermolite Liner

rated 4.5 of 5 stars
photo: Sea to Summit Reactor Plus Thermolite Liner sleeping bag liner

Limited warmth, but soft and comfortable to sleep in.


  • Soft fabric
  • Quality build
  • Adds some warmth
  • Nifty stuff sack


  • Heavy for warmth delivered
  • Expensive
  • One size fits all

I bought this product last winter to help out the warmth in a cheap sleeping bag, which it did slightly. Sea to Summit claims it will improve warmth up to 25 degrees F. I would guess this liner adds maybe 10 degrees of warmth.

I'm a big fan of Sea to Summit products in general, some seem a bit gimmicky or overbuilt but everything I've seen is well made, quality stuff. And this liner is no exception.

The liner is basically a soft fleece/flannel sheet, and it feels great on the skin. It's plenty long at 7 feet, and the material could probably be stretched even more to accommodate the average NBA player. As another review noted, its looseness and level of stretch can get you tangled up at times. It tapers up from a rather narrow bottom to a very large drawstring opening at the top. It packs up to about the size of a Nalgene.  

It's too heavy for me at 13.7 ounces to consider for backpacking when I'm looking for extra warmth:


The niche I've found for this liner is as a luxury item for 3-season use when I sleep in t-shirts and shorts. It's much nicer to sleep in the liner than directly on hammock, quilt, or sleeping bag material. I have used it as a stand alone "bag" in the summer, but I prefer a light quilt or even full bag that can be unzipped for this purpose.

It's a good product, but a real alternative would be to use a cheap flannel sheet and stuff it in a 5 gallon ziplock bag. If you're looking for warmth on the cheap, you'd be much better served buying a Double Diamond down throw or something similar.

The stuff sack is awesome. It's overbuilt, the black strap you see in the above photo is a handle! I like the way the drawstring runs back into the handle, too. Maybe I like the stuff sack more than the bag? Here it is hanging from the ridgeline on a summer trip, light ccf pad and this liner worked fine on a cool summer evening:

It's a neat and useful product if you're not on a budget and you're not too worried about weight.  

Source: bought it new
Price Paid: $65

Really warms up a bag when you are on the cold edge of what your sleeping bag can handle.


  • does what it says, warms up the sleeping bag


  • can get tangled up in the material

This bag liner is amazing. It really warms up the bag. I was camping with this and my Marmot Atom (40°) and the temps got down into the high 30s. I woke up in the middle of the night chilled so I slipped into this and immediately felt more warmth. Not long after I was getting really warm and had to vent my sleeping bag. I would never guess such a thin fabric would hold in so much heat.

The bag liner packs up pretty small. Not as small as a silk bag liner but not as big as a sleeping bag either. I am tall at 6'1" but this liner fit me just fine.  

On the down sides, you have to slide into this from the top and because it is a relatively thin material, if you toss and turn you can end up tangled up in it. Personally I would rather be warm than tangle free but that's just me.  Some might find it restrictive.  

I definitely recommend this liner for shoulder seasons or any time you are pushing your sleeping bags to their cold limits. Nice insurance to keep you warm through the night.

Source: bought it new
Price Paid: $55

This is a great addition to any sleeping bag OR used by itself.

My husband and I backpack a lot but did some car camping recently at Shenandoah NP.  I had just purchased the Reactor Plus at EMS and was super stoked to try it out. My husband, on the other hand, purhcased the cooler bag (poor choice). It dropped to about 49 degrees that night and I was VERY comfortable.

Although I'm ususally a cold sleeper, I slept the whole night thru with this one. (My husband, on the other hand, was a bit chilly.)

It is definitely worth the investment, especially if your current sleeping bag needs a little something to take the edge off during the cooler months. OR, if you're like me, and like to have a thin layer during the warmer(ish) months, but don't want to use an actual sleeping bag.

Price Paid: $50

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Price Current Retail: $69.95
Historic Range: $41.97-$69.95
Reviewers Paid: $50.00-$65.00
Weight 9.3 oz / 263g
Product Details from Sea to Summit »

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