The MummyLiner is a warm, lightweight, compact sleeping bag liner that extends a bag’s thermal rating


Size: 87 x 31-24″ (220 x 80-60 cm)
Rolled Size: 3 x 6″
Weight: 9 oz. (255 grams)
Temp Added: 9F (5C)

The Cocoon CoolMax Thermal MummyLiner is a warm, lightweight, compact sleeping bag liner that extends a bag’s thermal rating, and helps keep it clean and dry.

Campers who push the limits of their season—hitting the trail soon after the snow has melted or paddling until the ice sets in—often are compelled to keep a different sleeping bag for each season, to cover the range from sub-freezing temps to the heat of summer. The Cocoon CoolMax Thermal MummyLiner aims to help span that range by adding several degrees of warmth to your existing sleeping bag, and even serving as an ultra-lightweight standalone bedroll. How does it measure up?

First Impressions

The Thermal MummyLiner arrives packed snugly in its own tiny stuff sack, and its diminutive size makes one wonder just how warm it could possibly be. But like a silk handkerchief emerging from a magician’s sleeve, the MummyLiner soon lofts to its full volume, slightly broader than your average sleeping bag.

The CoolMax fabric is whisper-thin but, like most polyester knit technical fabrics, immediately begins reflecting heat when held in the hand. Soft, pliable, with a texture much like a wicking undershirt, the MummyLiner promises to be a comfortable bedtime companion. And, like most synthetic fabrics, should the MummyLiner ever become truly wet, it quickly dries with a gentle wringing and air evaporation.

The packed MummyLiner easily tucks away into an unused nook or cranny of your kayak’s cargo hold, barely larger than a 12-oz. can of Keweenaw Brewing Company’s Red Jacket Amber Ale.

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In Camp

If the weather warrants and you could use a bit of extra warmth in the sack at night, the MummyLiner simply slips inside your usual sleeping bag. Shimmy in, snug down the integrated neck drawstring, zip up your sleeping bag, and cozy in. I personally find the CoolMax fabric a bit clingy, which can make it somewhat difficult to squirm into, especially in the dark when returning from a midnight bathroom break, but it’s generally not a problem.

I also wish it had a zippered or Velcro side opening like a sleeping bag, for easier adjustment, but it can easily be pulled down to one’s waist for cooler sleeping.

The maker claims the MummyLiner boosts the temperature rating of a typical sleeping bag by nearly 10 degrees Fahrenheit, and this seems about right, in my experience. In the same way that I ‘layer’ my active-outdoor clothing depending on conditions, I do the same with my sleeping bag, adding thermal underwear and socks, perhaps a knit cap, sometimes even gloves, to adapt to the climate, and the MummyLiner has become a key part of this method.

The soft and comfortable CoolMax fabric is certainly warm in cold temperatures, but it also serves as a year-round sleeping-bag liner to protect your bag’s interior from sweat, skin oils, dirt and other trail grime, thereby prolonging its life. On those rare hot nights near the Great Lakes, I leave my sleeping bag stashed in the boat and sleep in the MummyLiner alone.

In The Long Run

After using the Cocoon CoolMax Thermal MummyLiner for a few years, from chilly early-season nights camped on the shores of Lake Superior to sweltering summer inland nights in a hammock, it has become an indispensable part of my camping kit. It packs so much versatility into such a compact package, that there’s no reason to leave it at home. I even take it when travelling in urban environments and sleeping in hotels with sketchy bedding.

All in all, for warm, dry, and clean sleeping, the MummyLiner certainly pulls its own weight.

Hits: adds warmth & versatility, provides comfortable wicking layer between you and nylon bag, compact & lightweight, prevents bedbugs in hotels
Misses: no side zipper, somewhat clingy

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