A warm, robust and comfortable camping mat for 3-season sleepouts

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad
(Image credit: Mark Mayne)

T3 Verdict

The Kelty Cosmic SI Mummy Sleeping Mat offers good warmth and a large sleeping area, but the penalty is weight and packsize. However, the build quality is strong too, making it a decent choice for the three-season camper.

  • +Good build quality
  • +Brass valve
  • +Large sleeping area
  • +Good R-Value
  • -On the heavy side
  • -Bulky packsize

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The Kelty Cosmic SI Mummy Sleeping Mat is a self inflating camping mat that takes aim at all levels of camper, and in three of the four seasons to boot. Available now, the Kelty Cosmic SI Mummy Sleeping Mat is priced at a UK RRP of £69.99.  

 Kelty Cosmic SI Mummy Sleeping Mat Review: Design and build 

The Kelty Cosmic SI Mummy Sleeping Mat follows a familiar pattern to many ‘self inflating’ sleeping mats, with an outer fabric shell and a foam inner layer that inflates the mat when unrolled. The outer fabric is 20D nylon ripstop and feels fairly robust to the touch, and another strong point on the robustness scale is the valve, which is made from brass – not lightweight, but certainly robust. Sometimes, however, a little extra weight is worth carrying for reliability at the end of a day on the trail. Read on to see where this sleeping pad fits into the best camping mats available today.

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad

(Image credit: Mark Mayne)

The Kelty Cosmic SI Mummy Sleeping Mat is an unusually generous 198 x 60 x 2.5cm when unrolled, and packs down to a standard-if somewhat chunky 31 x 21cm roll – with some help from a pair of elasticated straps. 

The mat gets an ASTM R-Value of 3.9 – that’s based on the new (2020) R-value measurement standard, snappily known as ASTM F3340-18. On the flipside, the weight of the Kelty Cosmic SI Mummy Sleeping Mat is headed precariously close to the kilo, weighing in at a stolid 920g (excluding stuff sack).

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad

(Image credit: Mark Mayne)

Kelty Cosmic SI Mummy Sleeping Mat Review: Performance and comfort 

Comfort is very much the watchword for the Kelty Cosmic SI Mummy Sleeping Mat, as there are no concessions to anything else, like lightness or packability. The unbroken foam sheet inside supports just like a mini-mattress, and the quilted surface effect adds a touch of luxury. There’s no cutouts in the foam, which gives a consistent mattressy texture, and the fabric isn’t unpleasantly slick. The generous sleeping area is also useful (as long as your tent floor is big enough), helping to prevent the dreaded ‘night-time rolling off onto the cold floor’ issue all campers will be familiar with.  

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad

(Image credit: Mark Mayne)

The Kelty Cosmic SI Mummy Sleeping Mat self-inflates in about 30 minutes or so, needing a couple of puffs to firm it up, like most similar mats. The brass valve is a strong point – a simple twist-lock plastic collar is easy to operate and intuitive, even in the dark. The metal construction should easily outlast the rest of the mat too, and in fairness cheaper mats often suffer from valve issues, so props to Kelty for nipping that potential issue in the bud. 

Performance is a bit more of a mixed bag – the ASTM R-Value of 3.9 is perfectly respectable for three season use, and indeed could at a bit of a push be used in winter, perhaps with a cheap closed cell foam mat. The problem really is the weight, which at just under a kilo is on the heavy side. Of course, for car camping and short trips this isn’t an issue, but at this price point you could easily pick up a Thermarest Prolite Three (for example) and save at least 200 grams for a similar sized mat for just £20-ish more. Or indeed try a Vango Trek Pro 3 Standard Sleep Mat, and save weight and a chunk of cash. 

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad

(Image credit: Mark Mayne)

Kelty Cosmic SI Mummy Sleeping Mat Review: Verdict 

As mentioned above, the Kelty Cosmic SI Mummy Sleeping Mat really falls down on weight and price, being quite heavy and getting dangerously close in cost terms to some of the premium mats available. In itself, the Kelty is a perfectly decent mat, and certainly seems built to last, which is a key concern both for the wallet and the environment.  

kelty cosmic si mummy sleeping mat review: a warm, robust camping pad, Outdoors, Kelty Cosmic SI Mummy Sleeping Mat Review: A warm, robust camping pad

(Image credit: Mark Mayne)

The R-value is enough to cover off most casual camping needs with ease, and the robust valve is ideal for the slightly less careful campers, and family-style environments. Overall it’s up to Kelty’s usual quality standards, but on the heavy side for backpacking and trekking applications.  

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