by the Product Review Staff | 2001-06-25 03:00:00-06
On seemingly rare occasions, large manufacturers get a wild hair to buck the system and offer a product that is so uniquely innovative that it does little more than incite snickers and scowls from traditional backpackers so ingrained in their ways that they aren't even willing to consider the possibilities of such innovations in design. The Elite Top Bag from Rab Carrington of the U.K. is one such example (Figure 1). The Elite Top Bag is marketed both as an overbag to extend the comfort of a lighter bag to colder conditions, as well as a lightweight 2/3 season bag. This review focuses solely on the use of the Elite Top Bag as a standalone bag.
|FIGURE 1. Rab Carrington's Elite Top Bag|
The concept behind the Elite Top Bag's design is a simple one. Insulating materials such as down depend on their ability to "loft" (i.e., trap air within their fiber interstices). Thus, since the insulation on the bottom layer of a sleeping bag is compressed by your body weight while lying down, then it effectively provides little or no insulating value (hence the need for an uncompressible foam sleeping pad for insulating the body from conductive heat loss to the cold ground). The Elite Top Bag forgoes an insulated bottom, replacing it with a single layer of open-weave mesh. The end result is a down-fill bag rated to near-freezing temperatures whilst weighing a remarkable 19 ounces!
The mesh bottom of the Elite Top Bag is 22" in width and extends 58" from the head end of the bag towards the footbox. Consequently, the bag retains insulated "sides" and a fully insulated footbox. The size of the mesh corresponds (approximately) to the dimensions of a typical ¾-length sleeping pad, so that cool air drafts entering the mesh are (in principle) minimized. Other weight saving features on the bag include no hood with a simple drawstring-and-toggle closure (Figure 2) to control drafts in the neck and shoulders region, and no zipper, requiring the user to wriggle in and out of the bag through it's opening at the head end.
|FIGURE 2. A drawstring closure and generous shoulder girth provides a good neck seal that controls drafts and retains heat in the head end of the bag.|
The Elite Top Bag is manufactured with 3-inch vertical baffles (the baffle material is an ultralight parachute nylon) spaced at intervals of 3.5 to 6.5 inches (with no obvious rationale regarding the baffle spacing!) in a narrow box construction. Approximately 7.1 oz of 750+-fill down is distributed among the baffles, which loft to a height of 2.0 inches at the baffle seams and 2.5 inches at the baffle mid-points (note that since the actual loft is less than the vertical baffle height, the Elite Top Bag can accommodate additional overfill for colder sleepers). The manufacturer suggests a temperature rating of approximately 32 °F. The shell material is a mini-ripstop (1.7-mm ripstop interval) nylon in the Pertex Microlight family (1.3 oz/yd2) of products from Perseverance Mills, Ltd. The mesh bottom is an open-weave nylon mesh with a fabric weight of 3.1 oz/yd2. The length of the bag is 67 inches, with interior shoulder, hip, and foot girth measurements (as measured) of 61 (measured at the head of the bag), 53 (measured at the midpoint), and 43 inches (measured one foot from the end), respectively. The manufacturer's reported weight of the Top Bag is 550 g (19.4 oz). We verified the weight of our sample to be 19.00 ± 0.05 oz.
TABLE 1. Elite Top Bag Specifications
|Shell Material||Pertex Microlight mini-ripstop, 1.3 oz/yd2|
|Insulation||Goose Down, 750+ in3/oz|
|Fill Weight (1)||7.1 oz|
|Baffle Material||Parachute Nylon, 1.2 oz/yd2|
|Baffle Height||3 inches|
|Measured Loft (2)||2.25 inches|
|Footbox Loft (3)||5.0 inches|
|Inside Girth||61" / 53" / 43"|
|Packed Size||11 x 24 inches (264 in3)|
|Total Weight (4)||19.0 oz (19.4 oz)|
|Notes: (1) Fill weight as reported by manufacturer. (2) Loft of top layer measured as the average of the loft measured at the baffle seams and baffle midpoints. (3) Average loft of footbox region (both top and bottom layers). (4) Weight as measured on a calibrated digital postal scale (weight in parenthesis indicates weight as reported by manufacturer).|
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.
There are too many variables involved that influence user comfort, including not the least, intrinsic metabolism and physiology, which vary greatly from user to user. Consider also that an individual user may sleep warm one night while sleeping cold another night, even when environmental conditions and sleep systems are equivalent, and the mere concept of temperature ratings becomes somewhat unjustifiable. Add to all of this the effects of a user's daily caloric budget (calories consumed vs. expended), clothing worn, and amount of moisture in a sleep system (e.g., from condensation of perspiration vapor), and you have a process of such complexity that it has baffled the world's best physiology modelers for years.
Thus, to "rate" a sleeping bag would be a hopeless exercise and to compare a manufacturer's rating to real-world performance based on experiences of a handful of testers would not only be unfair to the manufacturer, it could possibly lead to a false conclusion by a reader that did not fit the physiological profile of our testing corps or did not experience the same conditions that we experienced in our tests. Consequently, the best we can do is to measure the loft of the bag, and ask you as an informed consumer to compare it to the loft and temperature ratings of bags from other manufacturers in order to make a wise decision.
First, let's consider a comparison of the Elite Top Bag vs. those from other manufacturers with a similar loft on their top layer (Table 2).
TABLE 2. Comparison of Elite Top Bag with Sleeping Bags
with Similar Loft of Upper Layer from Major US Manufacturers
|Bag||Loft (in)||Temp (ºF)||Weight (oz)|
|Rab Elite Top Bag||2.3||32||19|
|Western Mountaineering Iroquois (1)||2.0||38||24|
|Marmot Hydrogen (1)||2.7||30||23|
|Feathered Friends Rock Wren (1)||2.0||30||28|
|Notes: (1) Hooded mummy designs.|
The data in Table 2 show that the manufacturer's suggested temperature rating for the Elite Top Bag is within a reasonable range of temperature ratings from other manufacturers when compared to bags having a similar amount of loft on the upper layer, so it is not unreasonable to expect that the Elite Top Bag is rated appropriately. However, one should keep in mind that the presence of the mesh (which could introduce drafts or result in heat loss for a sleeper that tends to roll) and the absence of a hood should be considered to decrease the comfort of the Elite Top Bag relative to a mummy bag having a similar loft on the top layer. Consequently, the use of a hat or balaclava, and/or a sleeping bag liner or clothing, should be expected to fairly extend the comfort range of the Elite Top Bag down to its estimated temperature rating.
We are testing the Elite Top Bag during the period April 1, 2001 to September 30, 2001. We've had the opportunity to evaluate the bag on seven nights in the field during two backpacking trips and have been pleased thus far with its performance at temperatures ranging from the mid-30s to the low-50s. To date, we've used the bag in conjunction with a tent or bivy sack/tarp combination, both of which serve to reduce, but not eliminate, the possibility of heat loss through the open weave mesh bottom. We've found this to be most uncomfortable (but tolerable), of course, when temperatures were in the 30s, while the effect was not noticeable for temperatures in the 40s or higher. The draft effects were most significant in a tent, with a bivy sack being much more effective at controlling heat loss through the mesh.
The key design flaw that needs to be addressed focuses on the shape of the bottom mesh material relative to the bag. Because the mesh is a 22" x 54" rectangle, and because the bag is tapered toward the foot, there is not enough side insulation near the foot end of the mesh, where drafts are most noticeable (see Figure 3). We found heat loss to be most significant in the lower regions of the bag, where the testers nearly unanimously complained of cold legs when temperatures were in the 30s. Because the bag tapers and the mesh panel does not, the effect of draft-sealing "sides" decreases towards the foot end of the bag.
|FIGURE 3. Bottom view of Elite Top Bag. Note the insulated "sides" and footbox, visible to the left/right, and top, of the mesh, respectively. In particular, notice the decrease in "side" insulation down the length of the mesh panel towards the footbox.|
The Elite Top Bag certainly has one of the highest warmth-to-weight ratios of any sleeping bag on the market. We were very impressed with its ability to maintain a remarkable level of comfort given its 19-oz weight. With a few modifications (see below), it just may approach perfection for the hardy backcountry traveler who is serious about shaving ounces.
To overcome the effect of the mismatched shape of the mesh and bag, the bag could be rectangular, and thus, provide "sides" down the length of the mesh (see Figure 3). A rectangular bag would increase weight unnecessarily while providing a less efficient shape, so a better option would be to taper the mesh panel to match the taper of the bag (i.e., a width of 22" at the head end of the panel tapering down to approximately 16" at its food end). To make this work, that part of the mesh panel that was "removed" so to speak, would need to be replaced by extending the width of the down-filled baffles down the length of the bag.
Another recommendation to save weight without losing function is to replace the mesh with a lighter material, such as Pertex Microlight taffeta (1.3 oz/yd2). This would help control drafts, as the open weave of the mesh material is particularly prone to convection currents. A possible disadvantage of this modification is an increase in "slipperiness", and consequently, less control in keeping the bag's insulation over you.
A final recommendation to the manufacturer: provide a stuff sack with the bag that is made of silicone-coated nylon (1.4 oz/yd2), instead of the heavy polyurethane-coated nylon sack that is currently provided.
The manufacturer's suggested retail price for the Elite Top Bag is £100. Rab does not sell directly to the public and currently, does not yet have a U.S. distributor. However, the Elite Top Bag can be ordered from Rock & Run, a U.K. retailer, either online or by telephone (http://www.rockrun.com/ or +44 (0) 153 943 2855).
"Elite Top Bag by Rab Carrington," by the Product Review Staff. BackpackingLight.com (ISSN 1537-0364).
http://backpackinglight.com/cgi-bin/backpackinglight/00045.html, 2001-06-25 03:00:00-06.