Ionosphere 5.5 Sleeping Mat – Regular

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Well made and offering excellent warmth-for-weight, the lonosphere will appeal to trekkers and mountaineers

Rab says: 

Crafted for extreme temperatures and hostile environments, the Ionosphere 5.5 is fully equipped with the tech to insulate you from the freeze. Its design reduces heat loss through both radiation and convection, thanks to the heat-reflective TILT technology and air-trapping Stratus™ R insulation. With a superior warmth-to-weight ratio and small pack size, it’s the perfect high-comfort sleep mat for alpinists and mountaineers who need to hunker down in the world’s most challenging conditions.

The mat features clever details to maximise your comfort, including oversized outer chambers to keep you central on the mat, and a grip print to reduce sleeping bag slip. The fabric has a soft next-to-skin feel while the versatile rectangular shape will ensure you can rest comfortably whatever your preferred sleeping position. A low-profile two-way valve and handy pump sack allow you to quickly inflate the mat when the temperature plummets and you’re ready to turn in.

Made from 100% recycled insulation, recycled fabric and a fluorocarbon-free DWR, the Ionosphere 5.5 is built to thrive in hostility. From frosty bivis to alpine starts, it will ensure you can comfortably restore reserves wherever you set up camp.

Our Verdict

This is a very comfortable mat, it’s 8cm thick, so works well for side sleepers; the two outer baffles are oversized, which helps to keep you on the mat if you are a restless sleeper. The rectangle shape, as opposed to a more tapered design, works better for me, as my legs always end up on the floor, losing heat.  The TILT (Thermo logic Lining Technology)  reflective film, which the mat is lined with, helps reduce radiant heat loss and improves the R-value, but most impressively doesn’t crunch or crinkle when you toss and turn; the mat is effectively silent.

It’s not the lightest mat in this price range; however, it is definitely the most robust, and is very well-made.

The pump sack is the most impressive I have seen; it inflates easily, holds a lot of air, and only weighs 71 grams. The elephant detailing is also a nice touch.   The flat-bottomed design takes up little floor space, so pumping it up in a confined tent is painless.  It took two and a half sacksful of air to inflate the mat fully.

I like the roll-away stuff sack. It’s an ergonomic design that, in principle, works really well; however, as is usually the case, it could be a bit bigger. Unless you are able to perfectly roll the mat away (and that just doesn’t happen in the backcountry), it won’t always fit back into the bag. For context, I used the Long Wide version of the mat, so this may not be the case if you use a regular size. A small grumble, I know, but it’s worth pointing out.

– Reviewed by Ultralight Outdoor Gear

Features

• 20D Recycled Polyester outer fabric with internal TPU Coating and fluorocarbon free DWR
• Stratus™ R 100% recycled polyester 200gsm insulation with TILT
• Stratus™ R insulation traps air and reduces heat loss from convective currents
• TILT reflective film within the insulation helps reduce radiant heat loss
• Lightweight construction uses air and insulation for superb warmth-to-weight ratio and minimal pack-size
• Oversized outer chambers helps keep you centralised on the mat
• Graduated grip print finish on upper fabric reduces sleeping bag slip
• Hybrid rectangular shape allows various comfortable sleeping positions
• Low profile two-way valve for easy inflation and deflation
• Pump sack included for rapid and hygienic inflation

Specifications

• Weight: 703g
• Dimensions: 183x51cm.
• ASTM R-Value: 5.5
• Thickness: 8cm
• Packed Size: 24 x 12cm 

ASTM R-Value

From 2020, there is a new industry standard for measuring the R-value (level of insulation) of sleeping mats – ASTM F3340-18. This new standard is the sleeping mat equivalent to the EN rating for sleeping bags.

You can now directly compare the R-value of mats rated using the ASTM F3340-18 with confidence that is a fair and accurate comparison between mats. In simple terms, the higher the R-value, the warmer the mat.

In general terms, an R-value below 2.0 is for summer use, 2.0 to 4.0 is for cooler 3 season use and 4.0+ is for winter temperatures. This will be also be dependent on your sleeping bag, how cold you sleep etc. Please contact our customer service team if you need advice on choosing the right mat for your activity.

Material & Construction

• 400T/20D 100% Recycled Polyester TPU coated

Help & advice:

• The Ultimate Guide to Choosing an Ultralight Sleeping Mat
• Time-Saver Guide to Choosing a Sleeping Mat
• About Rab
• Rab Sleeping Mat Guide
• Rab Sleeping Mat Technology Explained
• Rab Sustainability and Responsibility
• R-Value Explained
• Recycled Content in Outdoor Gear