Ultrasphere 4.5 Sleeping Mat – Regular Ultralight Airbeds

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The Rab Ultrasphere 4.5 is an ultralight sleeping mat made for cooler climates. It is warm and packable, weighing only 372g. It has a tapered mummy shape and includes an inflation pump sack.

Rab says: 

Combining TILT, ultralight fabric and heat-trapping offset air chamber construction, this featherlight air mat offers superb warmth for weight and packability. Highly comfortable, it’s the ideal foundation for thru-hiking and multi-day mountain runs.

When both warmth and low weight are crucial, the award-winning Ultrasphere 4.5 is the ultimate packable, featherlight air mat. Its ground-breaking design includes two layers of heat-reflective TILT, which reduce radiant heat loss, and offset air chambers that trap heat within the construction, allowing you to recharge comfortably without the need for high-volume insulation. Combined with a soft, exceptionally lightweight fabric, the mat’s weight-saving construction makes it ideal for bikepacking, thru-hiking, and multi-day mountain running.

With a comfortable tapered mummy shape that eliminates unnecessary bulk, the mat is thick and supportive, so that you can catch vital rest and restore the energy reserves needed for your action-fuelled days on the trail. When it’s time to pitch for the night, the low-profile two-way valve and inflation sack make camp setup quick and easy.

Featuring an included repair kit and unrivalled warmth-to-weight ratio, the Ultrasphere 4.5 is honed for fast-paced exploring in demanding mountain conditions.

While compatible with any sleeping bag, the Ultrasphere 4.5 can be paired with our Mythic Ultra 120 Modular bag to form an ultralight sleep system weighing around 700g.

Our Verdict

The Rab Ultrasphere 4.5 is an ultralight yet swarm sleeping mat designed for weight-conscious adventures in cooler conditions. Weighing just 372g it utilises innovative offset air chambers and dual layers of radiant heat-reflective TILT to maximise warmth without bulky insulation. The result is an impressive R-value of 4.3 in a highly packable design.

The 20D recycled polyester fabric keeps things light yet durable. The tapered mummy shape eliminates excess material and bulk. Inflation is easy with the included pump sack and the low-profile two-way valve. The warm yet feathery weight and compact packed size can’t be beaten for multi-day pushes.

I appreciate the provided “roll-away” stuff sack that holds the mat. While I wish it were slightly larger, it’s adequate for a leisurely roll on flat ground. However, when packing in a hurry inside a tent, it’s a bit too small.

– Reviewed by Ultralight Outdoor Gear

Features

• 20D Recycled Polyester outer fabric with internal TPU Coating and fluorocarbon free DWR
• 2 layers of TILT reflective film help reduce radiant heat loss without adding weight or bulk
• Offset weight saving internal cut outs help disrupt the flow of convection currents and keep warm air static
• Tapered mummy shape to save weight
• Low profile two-way valve for easy inflation and deflation
• Pump sack included for rapid and hygienic inflation
• Roll-away stuff sack with repair kit included

Specifications

• Weight: 372g (excluding bag)
• Pump Sack Weighs: 65g
• Dimensions: 183cm x 51cm
• Thickness: 8cm
• Packed size: 18 x 9cm
• R-Value: 4.3

Material & Construction

• Main: 20D 100% Recycled Polyester TPU coated

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.

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