Rab Quantum Top Bag Sleeping Bag REVIEW

The original top bag is state-of-the art in some ways, and an antique in others.

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by Will Rietveld and Jay Ham | 2005-11-08 03:00:00-07

Overview

The Rab Quantum Top Bag is a 32 °F (0 °C) minimalist top bag weighing only 16.0 ounces (454 g, regular width). Its light weight is the result of a simplistic design: no zippers, draft baffles, hood, or bottom insulation. The Q-Top is a top bag, designed to be used in conjunction with a sleeping pad to provide insulation on the bottom. We found a lot to like about the Rab Quantum Q-Top, but we also found some major design problems that wrecked its ratings.

Rab Quantum Top Bag Sleeping Bag REVIEW - 1
The Rab Quantum Q-Top is a minimalist top bag with no zipper, draft baffles, or hood. The bag’s outer shell, inner lining, and single layer bottom are Pertex Quantum. Weight of the standard width bag is only 16 ounces.

In Brief

  • Minimalist 32 °F top bag with no zipper, draft baffles, or hood
  • Weighs only 16.0 ounces (regular girth bag)
  • Pertex Quantum outer shell (with DWR) and inner lining
  • Insulated with 200 grams (7 oz) of 850+ goose down using narrow box-wall construction
  • Bottom (uninsulated) panel is too wide for standard sleeping pads and doesn’t seal, resulting in serious heat loss
  • Regular girth is too tight with pad inside, consider attaching pad to the bottom or getting the extra wide bag
  • Long and short sizes are not available

Specifications

  Manufacturer

Rab Carrington Ltd

  Model

Quantum Top Bag

  Type

Top bag

  Size and Style
Both sizes reviewed

Regular length and girth, regular length/extra wide girth, mummy style, hoodless, zipperless

  Weight

  Backpacking Light measurements oz (g) Manufacturer Specification oz (g)
Regular length, Regular girth 16.0 (454) 15.2 (430)
Regular length, Extra wide girth 17.4 (493) -

  Stuff sack Dimensions and Weight

5 in x 9.5 in (13 x 24 cm), 187 ci (3.1 L)

  Fill Type

Down, 750+ EU (850+ US)

  Fill Weight

7 oz (200 g)

  Loft

Backpacking Light measured single layer loft 2.5 in (6 cm)

  Manufacturer's Rating

32 °F (0 °C)

  Fabrics

Outer shell is Pertex Quantum with DWR, 0.9 oz/yd2 (30 g/m2); lining is Pertex Quantum, 0.9 oz/yd2 (30 g/m2)

  Hood

No

  Features

Narrow box-wall construction with variable height baffles, elastic drawcord at neck

  Model Year

2004

  MSRP

£130 (approximately $250 US) for the regular girth bag; £136.50 (approximately $260 US) for the extra wide bag

Features

Reviewing the upgraded Rab top bag was a bit nostalgic for the Backpacking Light staff, because our very first review was of the original Rab top bag. At that time the bag had a Pertex Microlight shell (1.3 oz/yd2) and lightweight mesh bottom. Back then it was state-of-the-art and a trend setter. How does the current version of the classic Rab top bag shape up in today’s market? Just a hint - Rab fixed one problem, and we wish they had listened to our other suggestions.

The current Rab Quantum Q-Top is a minimalist top bag in every way. It's a uniformly tapered mummy-style bag with no zipper, hood, or draft baffles; just an elastic drawcord that snugs the bag around your neck. Insulation covers the top, sides, and underneath the feet. Most of the bag's bottom is a single layer of fabric, so the bag must be used in conjunction with a sleeping pad to provide insulation on the bottom (more on that issue in the next section).

The bag's outer shell and lining are Pertex Quantum, which is lightweight, soft, downproof, highly breathable, and durable. It's the present state-of-the-art for lightweight performance sleeping bags and clothing. The outer shell has a durable water repellent (DWR) treatment to resist wetting from condensation. We found the Quantum fabric slides easily on most tent floors, particularly on silnylon floors.

The insulation is as good as it gets - 750+ EU/850+ US fill power goose down. With narrow box-wall construction and variable height baffles for efficient down distribution, the 200 grams of down in the Q-Top produce 2.5 inches of single-layer measured loft. Other than its superb shell and high lofting down insulation, the Q-Top is notable for its lack of extra features, bringing the weight down to 16.0 ounces (the extra wide version weighs 17.4 ounces) for a 32 °F rated bag.

The Quantum Q-Top is available in regular length/regular width and regular length/extra width only. Other bags in Rab's Quantum series are available in regular length, extra long, extra short, and extra wide. The Q-Top comes with a water-resistant Pertex Quantum stuff sack that is properly sized for the bag, plus a cotton storage bag.

Rab's Top Bag Design

If you haven't used a top bag before, then getting the Rab Quantum Top Bag will cause some major puzzlement. There are no instructions on how to use it - especially whether the sleeping pad goes inside the bag or under it (we clarify all this in our Review Summary). According to Rab's website, the Q-Top "is designed to be used on adventure races, mountain marathons and minimalist backpacking trips in conjunction with an insulating pad that is best cut to the shape of the bag (or for the hard core use bubble wrap!)". If you interpret Rab's "instructions" literally, it would mean that you would have to acquire a piece of wide closed-cell foam (not readily available) and cut it so it is a little wider than the bag's 22-inch wide uninsulated bottom panel, so it makes a good seal on the sides. That's okay, but nowadays most hikers use a sleeping pad that is a standard 20 inches wide.

Table 1: Comparative data for the Rab Quantum Top Bag regular girth bag and extra wide girth bag
  Regular Length/Girth
Backpacking Light measurements
in (cm)
Regular Length/Extra Wide Girth
Backpacking Light measurements
in (cm)
Shoulder Girth 62.1 (158) 70.0 (178)
Hip Girth 53.3 (135) 65.5 (161)
Foot Girth 36.5 (93) 50.5 (128)
Length 68.8 (175) 68.8 (175)
Sleeping Pad Panel 21.8 W x 58.5 L (55 x 149) 25.5 W x 58.5 L (65 x 149)
Insulation Width at Top 40.3 (102) 44.5 (113)

We found three major problems with the Q-Top: 1) with a thin sleeping pad inside, the regular girth bag is too tight (especially at the hips), resulting in compressed down and cold spots if you are wearing anything more than a base layer; 2) the uninsulated bottom panel is too wide, so there is serious heat loss around the perimeter of a standard width sleeping pad through the single layer fabric bottom; and 3) when using a pad outside and underneath the bag there is no means to seal the bag's insulation to the sleeping pad to eliminate cold spots. The sides of the sleeping bag pull up from the pad exposing a perimeter of single-layer uninsulated fabric.

The anomaly is even greater for the "extra wide girth" version of the Q-Top, because the width of the bottom panel grows from 21.8 inches to 25.5 inches. This creates a large uninsulated gap around the sleeping pad, resulting in serious heat loss and cold spots.

The upshot of this is that a sleeping pad inside the regular Q-Top simply doesn't work; it must be placed underneath, and there is no provision to attach it to the bottom and seal it to the insulated top. The bag lifts up from the pad, exposing the uninsulated bottom panel. A thin standard width sleeping pad can be used inside the extra girth Q-Top, but the extra wide bottom panel leaves 3 inches of uninsulated space on each side, and there is no easy way to seal it up. If you use the extra girth bag and custom cut your pad you can effectively seal the bottom, but the extra pad width adds unnecessary weight.

Rab Quantum Top Bag Sleeping Bag REVIEW - 2

Rab Quantum Top Bag Sleeping Bag REVIEW - 3

Rab Quantum Top Bag regular girth bag on top of the extra wide bag (left). The bottom sleeping pad panel of the regular Q-Top bag is 2 inches too wide (right), and the extra wide bag's panel is 6 inches too wide for a standard 20-inch wide sleeping pad. The girth of the insulated top is not enough to put a sleeping pad inside the bag, and there is no provision to seal the insulation to the pad when the pad is outside the bag.

Another issue with the Rab Quantum Top Bag is its limited insulated shoulder and hip girth, measuring only 40.3 inches on the regular bag and 44.5 inches on the extra girth bag. In contrast, the Nunatak Arc Ghost top bag has an insulated shoulder girth of 46 inches (it also has two straps to snug the insulation against a sleeping pad).

The Rab top bag was the first one on the market, and the only change to the bottom panel that we know of since its inception is the switch from mesh to solid fabric. Apparently, the bottom panel design has not been updated. In our opinion, it is simply not an adequate design by today's standards. In the next section, we discuss how the Q-Top can be modified to make it perform better.

Rab Quantum Top Bag Sleeping Bag REVIEW - 4
Will side sleeping in the regular length/girth bag with a thin sleeping pad inside. The tightness at the hips compresses the down and opens the gap next to the sleeping pad. Both result in serious heat loss.

Our Modifications to Improve Performance

We attempted to modify two Rab Q-top bags (one regular girth and one extra wide girth). On the regular girth bag we opened the seam between the uninsulated bottom and insulated top in several places and sewed grosgrain loops into the seam. We attempted to use these loops to more securely seal a pad to the edges of the insulated top. On the extra wide bag we sewed a fold into the bottom panel to reduce its width to 20 inches, and added pad straps to the bottom. Putting the sleeping pad under the bag resulted in increased inside girth and provided a slip-free contact with tent floors.

The modification did not work well for the regular girth bag. To seal the pad to the insulated panel, we effectively had to reduce the width of the uninsulated panel to the width of a sleeping pad. The 1.8 inches lost made for a very tight fit inside the bag (remember, no zipper!) and some down compression resulted. For a side sleeper, there were still cold spots at the edges of the pad. We had better luck modifying the extra girth bag; it provided (barely) enough shoulder and hip girth to wear extra clothing inside.

Bottom line, the user should not be expected to modify a product, or adapt to its shortcomings, to make it work. Rab needs to increase the girth of the insulated top and redesign the bottom panel so it seals a sleeping bag to the top without leaving uninsulated gaps.

Rab Quantum Top Bag Sleeping Bag REVIEW - 5

Rab Quantum Top Bag Sleeping Bag REVIEW - 6

The Rab Quantum Top Bag's problems can be improved by sewing a fold in the uninsulated bottom panel of the extra girth bag (left) to size it to your sleeping pad, and adding simple grosgrain straps to attach the pad to the bottom of the bag (right). This only works with the extra girth bag, which can be narrowed without becoming too tight.

Performance

Will (6', 170 pounds) slept in the Q-Top regular girth bag using three different sleeping systems (double wall tent, single wall tent, and bivy) on several backpacking trips in the Southern Rockies. Nighttime temperatures consistently dropped into the 28-35 °F range. On those trips a Therm-a-Rest Prolite 3/4-length sleeping pad (1-inch thick) was used inside the bag, and clothing worn consisted of microfleece long johns, windstopper fleece hat, and fleece socks. With this pad/clothing combination, the regular girth bag was way too tight in the hip area (see photo above), compressing the down at the hips and widening the gap between the pad and the uninsulated bottom panel of the bag, resulting in cold spots. The bag was warmer in the double wall tent or bivy, because of the extra shelter. The single-wall Tarptent was coldest on 30 °F nights because of nighttime breezes circulating through. Conclusion: placing a sleeping pad inside the regular girth Rab Q-Top does not work - it's way too tight.

Placing the sleeping pad under the Q-Top in the same sleeping systems significantly increased shoulder and hip girth inside the bag, which eliminated the problem of down compression and cold spots in those areas. However, wearing an insulated jacket inside the bag to extend its warmth resulted in a tighter fit and cold spots. Conclusion: this works better, but is still not good.

The unmodified wide-girth sleeping bag with pad underneath was warmer, despite an even wider uninsulated panel, because the extra width of the down top allowed the insulation to drape more like a quilt, sealing the edges somewhat. This worked fine on warmer nights, but the insulated top was not wide enough to tuck under the pad to seal the edges, creating cold spots on colder nights. Side sleeping while wearing an insulated jacket inside opened a gap next to the sleeping pad, creating some serious cold spots in the hip area. Wearing an insulated jacket plus insulated pants inside the bag helped to reduce the effect of the cold spots. Conclusion: this arrangement works on warmer nights, but it's hard to eliminate cold spots on a cooler night.

The modified wide girth bag with sleeping pad attached to the bottom was distinctly warmer than the above two options. The seal between the insulated sides of the bag and sleeping pad was much better, and the pad stayed in place quite well, even with frequent rollovers during the night. This configuration provided adequate hip space for side sleeping and room to wear extra clothing inside the bag. With the sleeping pad attached to the bottom, and wearing a down jacket and down pants inside, Will was able to stay warm in the Q-Top down to 23 °F while sleeping in a bivy. Conclusion: attaching the pad to the bottom of the modified wide-girth sleeping bag frees up some room inside, allowing one to wear insulated clothing inside the bag. The insulated clothing and attachment of pad to bag reduces the effects of cold spots along the sides of the pad.

Jay continued the review of Rab's regular girth Q-Top under the stars, under a tarp, and inside his homemade sil-pyramid tent (built with mesh sides like a Tarptent), in temperatures ranging from 45 °F to 28 °F. The unmodified regular girth Q-Top with a thin closed-cell foam pad (RidgeRest) inside worked marginally for Jay (5' 7", 155 pounds) on warmer nights, but only with minimal clothing and sleeping on his back or belly. Wearing heavier clothing or using a thicker pad caused down compression at the hips and accentuated the gaps next to the sleeping pad - the bag was simply too tight. Wearing a Western Mountaineering Flight Jacket inside the bag on colder nights gave minimal relief. Although cold spots were kept at bay, there was enough down compression in the jacket and bag to offset the expected improvement in warmth. In contrast, Jay has used the Flight Jacket under a quilt with equivalent loft into the low 20's with much better results.

Placing the pad under the bag mostly solves the girth problem. Jay was able to wear a synthetic fill jacket with minimal loft compression. However, lying inside the bag with the pad underneath allows the bag to lift up from the pad, exposing more of the uninsulated panel. Jay was able to sleep warm in lower temperatures with this configuration, but not at the temperature rating Rab assigns to this bag.

The modified regular girth bag, with sleeping pad attached to the underside of the bag at the insulated panel seam, sounds like the obvious solution, right? Well, not exactly. The uninsulated bottom panel is 21.8 inches wide. Attaching a 20-inch pad effectively reduces the total girth by 1.8 inches. While this may seem trivial, consider that the bag becomes more D-shaped (with the flat part of the D on the ground) rather than circular. The effect is compressed down at the top of the bag, made worse by side sleepers.

Conclusion: the regular girth Rab Q-Top is too tight, and it's hard to avoid cold spots. Either the insulation is compressed or cold air slips in along the edges of the uninsulated panel. Sleeping on your back or belly helps, but the bag needs more girth in the insulated top and some means to seal the top to a sleeping pad.

Our conclusion is validated by the ideal modification of the Rab Top Bag done by Alan Dixon, Backpacking Light's Product Review Director. Alan had the side seams along the bottom panel opened and extra insulated panels sewn in, increasing the bag's insulated girth. With this modification and a sleeping pad under the bag, he has eliminated cold spots and down compression issues and the bag now has sufficient girth to wear extra clothing inside.

With Rab's use of top-of-the-line materials and long-term experience with top bags, we expected better performance from the Rab Quantum Top Bag. No instructions were provided on how Rab expected us to use the bag. The problems lie with the design of the uninsulated bottom panel. Although it's obvious the bag is designed to put a sleeping pad inside the bag, there is simply not enough room inside for a sleeping pad and person. And there is no provision for sealing the insulated top to a sleeping pad underneath.

The Rab Q-Top top bag apparently retains an early design that is not adequate by today's standards, resulting in mediocre performance compared to other top bags on the market. Our modifications were enough to obtain acceptable performance and illustrate how the Q-top's performance can be improved by modifying the design. The Rab Quantum Top Bag clearly needs a re-design to efficiently and effectively utilize a sleeping pad for bottom insulation, and it can be done with minimal added weight.

Missing from this review (and for all sleeping bag reviews published here, for that matter) will be an assessment of whether or not the sleeping bag performs adequately at temperatures near its manufacturer-reported temperature rating. Click here for the complete Backpacking Light Position Statement on Sleeping Bag Temperature Ratings.

Durability

Pertex Quantum does not rank high as a durable fabric, but is more than adequate for this lightweight application. We observed very little down penetration through the shell fabric, and its DWR treatment kept condensation away from the down. Rab's narrow box wall construction works well to hold down in place; we did not notice any down shifting at all. Used in combination with a groundsheet or tent floor, the bag held up without incident through months of testing. With proper care, the Rab Quantum Top Bag should provide many years of ultralight warmth without failure.

Value

The Rab Quantum Top Bag is a "mixed bag," so to speak. We love it for its Pertex Quantum shell, high loft down insulation, baffle construction, light weight, and excellent seam work. If we consider materials and construction alone, and compare it to other similar bags from makers like Western Mountaineering and Nunatak, the Q-Top is an exceptional value. However, placing a sleeping pad inside the bag simply does not work, and the oversized bottom (uninsulated) panel creates unacceptable cold spots. Despite the agreeable price (approximately $250 USD) for an 850 fill down bag with a Pertex Quantum shell, the Rab Q-top barely rates an average value due to disappointing design flaws.

Tips and Tricks

Since this bag has no hood, it is important to wear a warm hat or balaclava to keep your head warm. If a buyer were willing to purchase the extra wide bag and modify it to fit a standard sleeping pad attached to the bottom, then the Q-Top would be a functional bag.

Recommendations for Improvement

With top of the line materials and a very competitive price, the Rab Q-Top would be an outstanding bag with a few modifications to the design:

  • Size the uninsulated bottom panel to snugly fit a standard 20-inch wide sleeping pad.
  • Devise a simple arrangement (such as two to three grosgrain straps) to attach a sleeping pad to the bottom of the bag. Anchoring these straps in the seam between the insulated and uninsulated panels will ensure a better seal against cold spots.
  • Increase the insulated girth of the regular cut bag to properly fit an average sized person (assuming bottom attachment of a sleeping pad). This would mean a shoulder girth of around 60 inches. The extra girth bag may need to be increased likewise.
  • Offer the Quantum Top Bag in extra long and extra short sizes in addition to extra wide sizes.

Citation

"Rab Quantum Top Bag Sleeping Bag REVIEW," by Will Rietveld and Jay Ham. BackpackingLight.com (ISSN 1537-0364).
http://backpackinglight.com/cgi-bin/backpackinglight/rab_quantum_top_bag_sleeping_bag_review.html, 2005-11-08 03:00:00-07.

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