In our previous reports on the very lightweight Sierra Designs Isotope rainwear, there was initial excitement, then disappointment when we discovered that it wasn’t waterproof, then encouragement when we found that most of the flaws had been corrected. In this review we evaluate the finished product.
Simply put, the Sierra Designs Isotope is the lightest woven fabric waterproof/breathable jacket currently available, and the pant is not far behind. Actually the Isotope is lighter than most non-woven fabric rainwear. More amazing yet is that it’s full-featured, not Spartan as you might expect.
The Sierra Designs Isotope jacket is the current lightweight champ, and it’s full-featured. The pant is slightly heavier than the 2007 GoLite Reed Pant, but it has a couple of extra features.
To be specific, the jacket and pants in size Large weigh 5.4 ounces and 5.6 ounces, respectively, for an even 11 ounces for the rainsuit. The pants are made of a slightly heavier Nanolite fabric than the jacket for greater durability. The jacket’s fabric weight is 1.17 oz/yd2, while the pants are 1.77 oz/yd2.
We can confidently say that the Isotope Jacket is the lightest rain jacket available today. The pant at 5.6 ounces is slightly heavier than the GoLite Reed Pant, which we previously measured at 4.4 ounces. However, the GoLite Reed Pant is being upgraded for 2007 with the addition of ankle zips, which will increase its weight to about 5 ounces. So the actual difference is small, and the Isotope Pant provides a couple of extra features (zip fly in men’s model, zippered rear pocket) for the extra weight.
Included in the 5.4 ounce weight for the jacket is an adjustable hood, full front zip with storm flap, two front zippered pockets, two inside drop pockets, full seam taping, and a hem drawcord. For the pants, the 5.6 ounce weight includes full seam taping, a zippered fly (men’s model), elastic waist drawcord, zippered rear pocket, and ankle zips with Velcro closures. Both men’s and women’s sizes are available
The Isotope jacket is loaded with features: Front pockets (top left) are huge and will hold a lot of stuff (the jacket stuffs into the left pocket), inside drop pockets (top right) are also large and very useful, the full-height #3 YKK front zipper (bottom left) has a storm flap with four Velcro patch closures, and the hood (bottom right) has a front drawcord with one adjustor on the right side.
The Isotope pant has 14-inch ankle zips with a Velcro tab closure. Will had no problem getting his size 12 clunkers through the pant legs.
On the utilitarian side, the Isotope jacket has a relaxed fit so it will easily layer over insulated clothing. The sleeves on the jacket are extra long, as are the legs on the pants. The hood fits well (especially with a billed cap), but has a drawcord adjustor on only one side which makes the hood feel like it is pulling to one side.
Considering its miniscule weight, the feature set of the Isotope is truly amazing. The zippered front pockets and inside drop pockets will hold a ton of stuff, which is really handy in camp. However they are not very useful on the trail because a backpack hipbelt wraps around all four pockets and limits their access. The full length #3 YKK front zipper is very effective for ventilation (it’s the only ventilation option when carrying a pack), but it’s fragile and won’t withstand rough use. To open the front zipper, it’s necessary to pull the four Velcro tabs open with the left hand while pulling the zipper with the right hand.
Sierra Designs’ Nanolite is a waterproof/breathable polyurethane coated nylon ripstop with DWR finish. The jacket is rated at 800 millimeter waterproofness while the pants are rated at 3000 millimeters. The higher rating for the pants means that they are very unlikely to leak when you sit on a wet surface.
Both jacket and pants have a moisture vapor transmission rate (MVTR = breathability) rating of 3000 g/m2/24 hours, which is at the higher end for a polyurethane membrane. The Nanolite fabric has the thinnest polyurethane membrane we have seen, which means that solid state diffusion through the membrane to the outer surface is faster.
So, what’s the catch? It could possibly be the jacket’s 800 millimeter waterproofness rating. That’s a little over 1 psi, which means that water under any more pressure than rainfall might go through it. Aestute readers will recall that Sierra Designs had some problems with previous versions of the Nanolite fabric not being waterproof, and a production flaw where the pockets were not seam taped. So, in this review of the “finished” version of the Isotope rainwear, it is important that we decisively determine that it is in fact waterproof.
In four months of field testing in normal rain and snow conditions, we didn’t detect any leakage at all. We further tested it by wearing the rainsuit over white cotton clothing in a warm shower at 30 psi – still no leakage. Finally, we rigged up a test to see if the jacket would leak under a simulated shoulder strap putting pressure on it in constantly wet conditions – no leakage again. So we conclude that the Isotope is in fact stormproof.
Sierra Designs’ Nanolite fabric (left) is a very thin smooth polyurethane membrane bonded to a thin ripstop nylon face fabric with DWR. All seams are taped. In our test simulating a weighted wet shoulder strap (right), no water leaked through the Nanolite fabric after 6 hours. The test consisted of a pair of wet socks tightened over the fabric with a webbing strap. We added water every half hour to keep it wet.
We wore the Isotope rainsuit in wind, rain, and snow in terrains ranging from desert to alpine. Overall, it gets high marks for wind- and waterproofness, and its breathability is as high as can be expected from its urethane membrane technology. (Photo by Rick Hagar.)
In use, we found that the Isotope’s breathability is decent but not exceptional. The breathability is simply constrained by the limitations of its hydrophilic monolithic membrane, which means that it’s not capable of transmitting moisture nearly as fast as it is produced under normal backpacking conditions. We found the jacket to be more comfortable and dryer inside when hiking slowly under overcast and cooler conditions, and wetter inside when hiking uphill while carrying a pack, especially under warmer conditions. Opening the front zipper helped a lot to exhaust excess moisture. Note that this scenario is typical of waterproof/breathable rainwear under backpacking conditions.
Since the Isotope is made of ripstop nylon it’s quite durable, but it’s definitely not bombproof. On the one hand, it’s much more durable than the non-woven polypropylene fabrics used in RainShield, DriDucks, and Frogg Toggs rainwear, but on the other hand you can’t go bashing through granite or multiflora rose with it either. It’s perfect for the average ultralight backpacker who takes reasonable care of his gear.
Overall, the Sierra Designs Isotope jacket and pants are the current champ for lightweight backpacking rainwear. Eleven ounces for a full-featured jacket and pants is amazing, and at that weight we will take the features and not bicker about how the manufacturer can shave a few more grams.
Features and Specifications
- Manufacturer: Sierra Designs
- Sizes: Men’s S to XXL, women’s XS to XL
- Jacket Features: adjustable hood, full front zip with storm flap, two zippered side pockets, two inside drop pockets, full seam taping, hem drawcord
- Pants Features: Full seam taping, a zippered fly (men’s model), elastic waist drawcord, zippered rear pocket, and ankle zips with Velcro closures
- Weight: Measured jacket weight size Large 5.4 oz (153 g), manufacturer specification 5.4 oz (153 g); measured pant weight size Large 5.6 oz (159 g); manufacturer specification 4.8 oz (136 g)
- MSRP: Jacket $90, pants $70