The second wave of sleep pads from the UK has arrived. Rab's new Ultrasphere 4.5 air mattress is "highly insulated, comfortable, lightweight, and affordable." It's still a must-buy

Last season, Rab, the British outdoor brand that introduced the Rab Ionosphere 5 ( see review) , delivered a sleeping pad with incredible performance at an affordable price, a first for the brand, and this season they have once again delivered a stunning new product.

This is the new sleeping pad from Rab that I'll be reviewing today: the Ultrasphere 4.5 . It's a feather-light mattress, but it's not just light; it's also packed with Rab's signature attention to detail, offering excellent insulation.

Thankfully, once again, they were kind enough to provide this mattress to our website with the condition that we were free to review it. I was able to try it out in a tent this season, so I would like to share my review with you

Main features of the Rab Ultrasphere 4.5

The Rab Ultrasphere 4.5 is an all-season inflatable sleeping pad that combines lightweight, compact design with excellent insulation. Weighing just 370 grams, it achieves a high R-value (warmth) of 4.3 thanks to its heat-reflecting TILT technology, making it suitable for year-round use. Its 8cm thickness, flat side baffles, and quiet design minimize friction when turning over ensure a comfortable, stress-free sleep, even on uneven surfaces. The slim 2-way valve allows for quick and easy inflation using the included pump sack. Despite its high performance, it remains surprisingly affordable.

Favorite points

• High insulation that lasts even during the snowy season
• Lightweight and compact, despite its high thermal insulation properties
• Sufficient thickness
• Flat baffle structure with moderate unevenness
• Serenity
• Grip print on the outer surface prevents sleeping bags and pillows from slipping
• Convenient 2-way valve system and dedicated pump sack
• Surprisingly low price for its overall performance

Points of concern

• The back fabric is slightly thin at 20D (but it is TPU coated, so it is stronger than just 20D polyester)
• If I had to say something, it would be that the cap is difficult to open when letting the air out

Main specifications and evaluation

Detailed Review

Insulation, weight and size: Unique insulation structure provides exceptional insulation performance relative to weight

The first thing that strikes anyone who picks up this mat is its lightness and compactness. It weighs just 370 grams, and when packed, it's much more compact than a Nalgene bottle. It's so light and small that a generation ago, it would have seemed like a summer-only model. For hikers looking for a tough adventure, the reduction in weight and storage size is a benefit that no one can ever be satisfied with

And yet, in terms of insulation (warmth, or how well the mattress resists heat loss), the most important spec of all, it has an ASTM R-Value of 4.3, a global standard that indicates the insulating power of a mattress. While this value is not high enough to be used exclusively in winter mountains, it is a well-balanced value that provides high insulation and versatility for use all year round, in spring, summer, autumn, and winter (snowy mountains)

This high level of balance is achieved by the use of a heat-reflecting film that uses our proprietary " TILT (Thermo Ionic Lining Technology) " technology, which reflects the heat generated by your body inside the pad to minimize radiant heat loss, and by using an offset baffle structure that prevents convection of heated air. The diagram below shows the arrangement of the baffles inside the mat and the air flowing through the holes in the baffles. The staggered arrangement of the holes prevents the air from flowing in a straight line, making it difficult for convection to occur.

The combination of these two mechanisms allows us to efficiently trap heat inside while minimizing weight and bulk, thereby achieving top-class "warmth per weight (or stored size)."

Comfort: The mattress provides a comfortable sleep with a basic flatness and a subtle wave that prevents slippage

Designed for a variety of mountain activities, from bikepacking through the mountains to high-altitude traverses and multi-week thru-hikes, this mat features a thin, lightweight 20-denier recycled polyester front and back, and is reinforced with an airtight TPU coating to maximize durability. While it's certainly not rock-solid, it's not so brittle that it'll tear apart with just a pebble. While some care is required, it's reassuringly safe to use in a tent with a floor

The shape is basically mummy-shaped, with no corners and tapered towards the feet, but the toes are not that narrow (see photo below)

surface

The back side. The air intake and exhaust ports are located at the foot of this side

The mattress is 8cm thick, so even side sleepers can sleep comfortably without touching the ground. You won't even notice uneven terrain, and you'll feel as if you're sleeping in a bed

the Ultrasphere 4.5 has a horizontal baffle structure with horizontal tubes. This style is flatter than a vertical baffle structure with fewer bumps and depressions, and even if weight is concentrated on one point, the surface feels more natural and comfortable when sitting or lying down than a vertical type.

Furthermore, the horizontal baffles themselves are gently wavy, making them slightly less likely to slip off when you roll over in your sleep

And (as I noticed with the Ionosphere 5), despite using a metal film, the rustling noise is still not at all bothersome, and the sound is quiet enough not to disturb your sleep

For this review, I spent one night in a tent in a low mountain (nighttime temperatures were around 3°C), and even though my back was directly pressed against the ground with a quilted sleeping bag, I felt almost no cold air from the ground. Of course, how you feel this will vary depending on the sleeping bag, but it seems like it would be versatile enough to use in combination with a sleeping bag in chilly seasons, or as a direct sleeper in the summer

Storage and usability: Surprisingly compact for this class

The Ultrasphere 4.5 is an inflatable air mattress. Naturally, you need to pump air into it in order to use it. As is not uncommon with recent high-end models, this model also allows you to pump air directly through your mouth, or you can easily inflate the mattress using the included special "elephant pump sack" (pictured below).

The air inlet is the Ionosphere (see photo below). It doesn't protrude much and is flat against the mattress surface, so it won't get in the way when you sleep or store it away. It's also durable, so you can rest assured.

I personally like the large capacity pump sack, and if you fill it to the brim with air, you can inflate it almost to the maximum with just 3 or 4 puffs

Cost performance: As always, amazing value for money

The Rab Ultrasphere 4.5 offers excellent performance, achieving surprising lightness and packable size without sacrificing superior insulation and comfort. But what's even more noteworthy is its price. As with last year's Ionosphere 5, we compared the key specs and prices of three popular sleeping pad models with similar R-values ​​(mummy-style air mattresses with R-values ​​between 4.5 and 5.0) (the gold background indicates the highest value). Each model has its own strengths, and the best fit for each individual may depend on what they prioritize. However, the Ultrasphere 4.5 stands out in terms of weight and packable size, and its price is also significantly higher than that of competing models. Considering that its shortcomings are largely negligible, its excellent value for money is not to be overlooked.

Comparison of major models of all-season mummy-style air mattresses 2024

Summary: Recommended for these people

I was quite impressed with last season's Ionospheare Ultrasphere 4.5 may even be even more impressive. Despite its ultra-lightweight, compact design—something Ionospheare The Ultrasphere 4.5 is suitable for a wide range of activities, from speed-prioritizing hikers and climbers to alpinists and cycle tourists, and is recommended for anyone who doesn't want to compromise on comfort, weight, or performance. On the other hand, for those who only need something lightweight, or who prefer comfort even if it's heavy, there are other options. If you've been thinking about getting a full-fledged air mattress that you can use for a long time, this may be the year. Be sure to pick one up and check it out at a store.

Combine it with the simultaneously released "Mythic Ultra 120 Modular Sleeping Bag" to create a lightweight, comfortable sleeping system suitable for three seasons, weighing under 700g

When combined with Rab's lightest down sleeping bag, the Mythic Ultra 120 Modular, which was released at the same time, you can create a lightweight sleeping system that weighs less than 700g and can withstand temperatures as low as 0°C

Of course, the Ultrasphere 4.5 is excellent as a standalone sleeping pad, but if you're looking to keep your overall equipment lightweight without compromise, this option is also worth considering. By the way, we'll be reviewing the Mythic Ultra 120 Modular on this site at a later date, so stay tuned

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