Among our staff, the Sierra Designs Isotope rain jacket at 4.4 oz was the talk of the show at Summer Outdoor Retailer. Since then it gained an ounce, but is still under 6 oz. Even better it has features that one would expect in a jacket twice its weight.
Changes in Nanolite line from summer OR
- Uses a more waterproof fabric* (see fabric specs below)
- Isotope weight goes up 25% (4.4 oz summer OR to 5.5 oz current version, due probably to a more waterproof fabric)
- Hoodless version, the Neutron jacket, dropped from the line
Even with an ounce weight gain, the Sierra Designs Isotope is still the lightest waterproof/breathable fabric rain shell on the market. Sierra Designs targets the jacket for what 95+% of US outdoor enthusiasts carry a rain jacket for. That is, short shower protection and done-in-a-day activities. Kudos to Sierra Designs for doing this for under 6 oz and for well under a hundred bucks. Compared to over priced, stripped down rain jackets designed for hardcore adventurers and climbers, the Isotope also has all the features that the average outdoor hiker expects — two zippered hand pockets, a full length front zipper with storm flap, and a full drawcord at the hem and hood opening. The jacket is as supple as many ultralight windshirts and compacts to a small size. I can stuff a large Isotope in my pants pocket.
The compromise? The Isotope’s fabric has only 800 mm waterproofness (many WP/B fabrics are around 10,000 mm). Sierra Designs claims that the Isotope jacket is made for light to short rain so don’t expect it keep you dry in a day long downpour. We found the recent version of the jacket kept water out with the exception of leaking pocket seams. The jacket should be reasonably waterproof all round once Sierra Designs corrects this problem in the next production run.
Since summer OR, we’ve had a chance to test two versions of the Sierra Designs Isotope Jacket. Our first sample used a less than perfected prototype fabric* (see more below) and was not completely waterproof in an hour long rainstorm. But it was a true 4.4 ounces! Since then Sierra Designs revised the fabric to have a heavier and more waterproof membrane.
The fabric revision seems to have worked. The new Nanolite fabric on our current test version is reasonably waterproof. In a hard 15 minute downpour I had no wet spots or leakage around the hood, shoulders and upper body—places that jackets normally leak. To my surprise, after about 5 to 10 minutes of good rain the bottom of the front pockets started to fill with water. Eventually the water wicked into my shirt getting it wet from the hem to above my navel. Upon closer inspection, I found that the pocket seams were un-taped. A call to Sierra Desings confirmed the manufacturing plant had neglected to tape the pocket seams on the Spring run of the Jackets. The Fall run of Isotope jackets will have taped pockets seams.
At 3,000 g/m2/day the Nanolite fabric is in the lower-to-middle of the pack for breathability. It is not as breathable as fabrics like Gore-Tex XCR or eVENT. Without any venting options other than a full length zipper this might not be the jacket for sustained uphill hiking in the rain.
The Isotope hood could use improvement. The single drawcord adjustment on the hood is difficult to operate. I had to cinch the drawcord a bit and then inch the hood fabric along the drawcord, re-cinch the drawcord, and repeat a number of times to finally close and even out the hood opening. One should probably adjust the hood at home or in camp, and then only make minor adjustments on the trail. Finally the jacket lacks a brim. For serious rain I used a billed cap in conjunction with the hood.
In summary, the Isotope trades some fabric waterproofness and breathability for weight and features. The current version of the Isotope jacket is probably a good light rain or shower jacket. For those that don’t mind a bit of leakage, it may suffice for more inclement conditions and longer periods. Once Sierra Designs fixes the leakage around the pockets in the Fall production version, it should be a much improved jacket — possibly doing a deal better in significant rain than Sierra Designs advertises.
Features and Specifications Jacket
- Manufacturer Specified Weight: 5.5 oz (156 g) Men’s large
- Backpacking Light test samples: 5.6 oz (159 g) and 5.2 oz (147 g) Men’s large
- Also available in a Women’s model, Mfr weight 4.4 oz Medium
- Price is still $89
- Available in March 2006
Specifications Nanolite Fabric
- 39g/m2 fabric
- Waterproof to a hydrostatic head of 800 mm
- 3,000 g/m2/day breathability
- PU microporous coating on fabric. (SD claims the membrane is microporous.) After application to the fabric, the PU membrane is lightly acid etched to eat pores in the PU membrane and improve breathability. (Note: the fabric in the first demo jacket last summer failed waterproofness. The manufacturer over acid etched the fabric and it had little or no PU left.)
- Retains 80% of its DWR after 20 washings
V22x17 D nylon Meryl ripstop