|Sea To Summit Reactor Extreme Sleeping Bag Liner adds 25 degrees and 14 ounces for the size of a red solo cup.
Not so fast. As autumn evenings grow cooler, that Mithril-light summer sleeping bag feels thin, sort of stretched, like butter scraped over too much bread, as Bilbo Baggins would say. I learn that its 30 degree temperature rating is directed to survival, not comfort. That is, most individuals will survive a 30 degree night nestled inside the sleeping bag. but not necessarily sleep well. I might want a little more margin of error for the higher elevations of the Rocky Mountains, even in summer.
Here in the Black Hills of South Dakota, I find that my 30 degree bag is comfortable sleeping at about 50 degrees, when wearing a single base layer. Ten degrees warmer drives me out of the sleeping bag. Ten degrees cooler adds a down hoodie and booties. So, all is good at about 40 degrees and up, with my standard kit. For a typical Black Hills summer, that's plenty of sleeping bag for me.
|Helmet, Sea To Summit Reactor Extreme Liner in a non-compressed stuff sack, Brooks Range Alpini 30 sleeping bag.
But what about nights when the temperatures drop into the 30's, or even the 20's? That's certainly possible over a 2,500 mile ride along the Continental Divide, even in August. And I'd like to have the option of bikepacking more during the spring and fall here. I search for options.
I start with 850+ fill down sleeping bags rated in the 5-10 degree range, thinking that would create a comfort range somewhere in the 20's. I like the specifications and reviews for the Kuiu Super Down 15, the Feathered Friends Lark 10 YF, and the Western Mountaineering Versalite 10. If my current bag needed replacing, I would consider one of those. But it seems silly to add a whole new bag, especially at about $600.
So, I move to light down over-bags and quilts with enough loft that, when added to my sleeping bag, match the 6 inch plus loft provided by the 5-10 degree bags listed above. There are many options, with the higher quality ones weighing nearly a pound and running about $300. Again, the added volume, weight, and cost seems high for the benefit.
|Sea To Summit ThermoLite Reactor Extreme sleeping bag liner, usable alone as a sleeping bag above about 60 degrees.
There has to be other options. One day at work, I mention my quandary to a trusted colleague, a retired Army Airborne Jump Master. He describes the Army layered sleeping system, which includes a removable, thin inner layer called a sleeping bag liner. He suggests I look there.
It doesn't take long. Many sleeping bag liners are designed for comfort, such as those made of silk or cotton. Others are designed more to protect the sleeping bag, such as those made of a woven synthetic. If those types of liners add any warmth to the sleeping bag, it's not noted in the marketing or reviews beyond about 5-10 degrees. That won't do.
Then I find the Sea To Summit line of "cold weather" sleeping bag liners that use a thin layer of fabric with hollow threads designed to add warmth to your sleeping bag. They offer four levels of liners, purportedly adding from 14 to 32 degrees. Even after reading glowing reviews, I am skeptical, given the relatively low weight, packed size, and price of these liners. So, I go old school shopping at a brick and mortar store.
|The orange liner stylishly tucks into my blue sleeping bag.
After spending enough time in the store to send Colleen to the nearest Starbucks, I finally decide to try the Sea To Summit Reactor Extreme Liner, which purports to add 25 degrees of warmth, weighs 14 ounces, packs to the size of a red solo cup, and retails at about $70. But it just seems so thin, so light, so small, and so inexpensive. Is it too good to be true?
Nope. This is the real deal. I'm comfortable sleeping in the low 30's with this liner inside my Alpini 30 sleeping bag, while wearing a single base layer. Without the liner at those temperatures, I am cold. I'm confident that this liner will extend my comfort zone into the low 20's, and then even lower when I add a down hoodie and down booties. It's a low cost insurance policy against unexpected cold weather and a season-extender, while adding less than a pound and fitting into my current sleep kit bag on my Jones Plus LWB.