Sea to Summit Reactor Extreme Thermolite Liner

Winner!

Occasionally I find a product that makes me ask "Why doesn't everyone use this?" This sleeping bag liner by Sea to Summit is one of those products. 

I was seriously worried when I heard the weather forecast for our Yosemite Adventure state "Low of 20 degrees in the valley" because my 30 degree MontBell would, at best, leave me shivering and could be downright dangerous at higher altitudes or if the weather turned out worse than planned! 
Contenders:
I seriously considered a last minute purchase of a separate 0 degree winter sleeping bag or supplementing with a spare Heetsheets Emergency Blanket by Adventure Medical Kits. But I don't like single-use items like winter-only sleeping bags and planning to use my emergency shelter seemed a bit of an oxymoron and completely against my philosophy of use.

Got Specs:

Size             L84" W36" (L210cm W90cm)
Weight        14 oz (399 grams)

What Wins:

1. Warm! This thin layer of Thermolite adds significant warmth to my existing bag. I can slip this liner inside my MontBell and be toasty warm - it will rival all but the most extreme winter bags. 
2.  Multi-use! Use it as a stand-alone sleeping bag in the summer so I don't sweat in my down-filled bag. Be comfortable and modest when staying in places with minimal extra bedding, like my sister's couch in Kansas City.
3. Clean! The liner protected my expensive sleeping bag from my skunky body when it was too cold to bathe in Yosemite. It protected me from la cucarachas when staying in a sketchy no-tell-motel where I was afraid to use the blankets or make contact with the mattress and Ben was afraid to sleep on the bed altogether.

What Fails:

1. Access! There is not a zipper on this bad boy so I have to wriggle in - which is difficult inside another mummy bag - or roll it up from my feet like a giant condom.
2. Cost! I paid $65 at REI for what amounts to a couple of square yards of Thermolite! I should buy a bolt of the fabric, a sewing machine and go into business. 
3. Name. Couldn't they come up with something more concise than Reactor Extreme Thermolite Liner? It sounds like a part to the space shuttle. I like the Under Armour method. When I buy Base 2.0 I know exactly what I'm getting and where it stands in their product line - warmer than 1.0 and cooler than 3.0. Simple.

Meh:

1. Ultra Light (UL)? Not exactly. But it takes up very little space and can be stowed separately from you main sleeping in your backpack.

Other notes:

1. If you have a 3-season sleeping bag I'd strongly recommend this over a separate winter bag. (Unless you need to get below zero!)
2. If you don't need it to bolster the performance of your regular sleeping bag for winter use I'm sure you can find less expensive alternatives - like a sheet!