Down has been a popular and powerful insulating material for a very long time, either in quilted form, found in sleeping bags or used in outdoor wear. Modern down jackets are lightweight and are hard to beat in terms of insulation – as long as the conditions are suitable. Under a hardshell jacket they are ideal as a mid-layer for keeping warm in cold and unpredictable weather, for summit rests, as a warm back up for other moderately strenuous alpine activities and as everyday apparel. Often, however, as you go into a sweaty ascent or climb, a down jacket may quickly lose its insulating effect as it becomes moist. For wet conditions or perspiration-prone activities an alternative insulation jacket with synthetic filling or a wool-based insulation is becoming increasingly popular. Both of these variants have superb warming properties even when wet, however, are a little harder and less compressible than jackets with down filling. New on the market are also waterproof down jackets with hydrophobic down.
Quality down: The loft says alot about the thermal capacity
As insulation material down is unbeatable in cold and dry conditions. The fine plumage of ducks and geese acts as filling in the down jacket as a buffer against the depth of winter: Between the down feathers, which have a three dimensional structure, countless small “air bubbles” store body heat, ensuring a highly effective insulating layer form. Because of its elasticity, down can be compactly compressed and amazingly quick to spring back to its initial volume. So it not only insulates especially well, but can be folded together into an extremely small packing size. Its compactness makes a down jacket, an ideal warm layer to throw into a backpack (some even fit into their own pocket) and with consistent proper care, will remain reliable for years to come.
The bulk or fill power/loft provides information as to the thermal capacity in accordance to the quality down. The measurement is given in cuin, (cubic inches e.g 1 inch³ = 15,62 cm³) this states which volume a compressed ounce (approximately 28.35 grams) of down expands to after an hour. Usually, 500-850 cuin is sufficient for a down jacket. A higher fill power means better thermal insulation in relation to the packing volume and therefore a warmer jacket. High-quality down jackets have a fill power of 700 to 800 cuin. To assess the quality of down, one can also orientate to the mixed ratio of down to smaller or supporting feathers – 95/5 means the fill is made from 95 percent down to five percent feathers. This, for example, would be a very high quality down fill.
Down jackets with chamber construction have an advantage
In order that the down fill doesn’t slip inside the jacket, it is sewn into chambers. There are two common design variations: stitch through seams and box chamber construction. With a stitch-through design, the outer and inner shell of the jacket is simply sewn together to create chambers; the latter separate chambers within the jacket are used. Quilted seams means an uncomplicated version and less weight, however, cold gaps can form along the seam and leave down not being able to expand there. For lighter models, this can be ignored as they are usually worn in milder temperatures, during intense activities or as a warm mid layer under a hardshell jacket. The warmest down jacket, ideal for double-digit minus temperatures and expeditions, are mobile thermal wonders, such as the Expedition Jacket from Rab, that hold the chambers in the down jacket not only on the spot, they also form a mainly, continuous insulating layer that is supported by both the chambers and seams rather than be interrupted by them. A more complicated process entailing more detailed workmanship than the stitch-through construction, also reflects on the price of such a down jacket.
Down and moisture
For warmth-weight ratio down can not be beat, however during high-pulse activity and wet conditions an insulation jacket with a synthetic fill has its advantages over a down jacket. When down becomes wet, it clumps together and loses most of its thermal efficiency. Most fabrics are only partially breathable so that perspiration isn’t absorbed by the down. So that down jackets can also be worn in wet conditions, manufacturers such as Dynafit, Mountain Equipment and Berghaus have developed waterproof down jackets, which are equipped with hydrophobic down. The Berghaus Ramche jacket, for example, has a Pertex® Quantum® water-repellent outer material; the down itself has also been finished with a special water-repellent treatment. Hydrophobic down absorbs 75 percent less moisture than untreated down, ultimatedly warming even under moist conditions. Another excellent example of this is the Millet Trilogy Down Hoody.
Synthetic fill alternative
Many labels now have available insulation jackets with an alternative to down fill made from synthetic fibers: Artificial down imitations are not quite as lightweight, packable and warm as down, but considerably less sensitive to moisture. Insulation jackets with synthetic fill such as the Direct Alpine Sella or Millet Trilogy are excellent for strenuous endeavors such as freeriding, cross-country skiing or ski touring, as well as for multi-day hikes without the possibility of drying. They are also suitable for more humid regions. Hybrid constructions like the Millet Touring Hybrid Down combine both down with breathable synthetic fiber materials for a superb climate balance while ski touring or for other intense activities.
In addition to widespread PrimaLoft fibers, other fillings exist, such as Polarguard, Thinsulate as well as own brand technologies from diverse labels such as Arc’teryx, The North Face, Patagonia and Marmot. Even the Polartec fleece manufacturer has designed the breathable insulating Polartec Alpha fabric – that can be found, for example in the Bormio jacket from Vaude.
Wool as insulation material
For those that can do without the smallest pack size and best warmth-weight ratio and are searching for a natural alternative to synthetic, should consider the virtues of a jacket with wool fill. These are also relatively insensitive to moisture and provide an ecologically sustainable basis for excellent insulation for strenuous mountain activities in winter. Ortovox is a pioneer in insulating jackets with pure new wool filling. The wool used derives from the brand Swisswool and the wool is produced from small Swiss farmers.
Further info relating to down and alternative fabrics:
- PrimaLoft: The smart alternative to down
- Merino Wool: the functional fibre in more detail
- Devold – merino clothing from Norway