Insulated Jackets - Basics, Features, and Materials
An insulated jacket must provide protection against the outside weather conditions. Keeping out wind and precipitation is the most important task of your outer layer. If this layer fails in heavy rain, it doesn’t matter how good your other garments are or what material they have been made of - wet clothing exposed to the wind can bring you on the verge of hypothermia very rapidly. Your insulation jacket must be waterproof - it’s much more comfortable if it is made with waterproof breathable fabric (WBF) such as Gore-Tex, eVent or another material of this kind so that the jacket will allow moisture transfer from the body to the environment in order to avoid excessive sweat accumulation.
Clothing helps you stay comfortable by creating a thin insulating layer of air next to the skin. The enemies of comfort work against this protective air layer. An outerwear will protect you from environmental factors such as wind, rain, and snow and will also add to the total insulation. However, don’t expect too much from your insulated jacket. In heavy rain, you will be well protected and will remain relatively dry, though, in prolonged wet conditions, you’ll get wetter with time because of two reasons: 1) the high humidity will restrict the fabric’s breathability and 2) you won’t have enough time to dry your clothing.
Make sure your outer layer is roomy enough to accommodate all your other layers underneath. In consistently wet conditions you need all three layers of your clothing to work as a system, so a moisture-wicking and quick-drying base layer and a breathable fleece can make a difference. As you learned from our post about fleece fabrics, a fleece will keep you warm even when damp and it dries quickly as well.
Softshells and softshell jackets sometimes can replace insulation jackets, especially for day hiking or city walking in better weather conditions. Softshells are water-repellent and wind-resistant, flexible and air permeable, meant to protect you until you find shelter. Softshells excel at maintaining a comfortable temperature during high exertion and are exceptionally mobile, moving freely and easily, though you can’t rely on them in extreme conditions. Hardshells, on the other side, are fully windproof, waterproof and breathable - made to protect you in harsh weather conditions.
An insulated jacket as part of a layered clothing system
Obviously, it’s clear that each layer of a clothing system must be analyzed separately. In addition to that, it’s also important to analyze the interaction between different layers in a clothing system. Therefore, the whole layered clothing system must be examined as a solid construction and not only as a sum of its parts. Doing only the latter would be a mistake because layering of the different fabrics has a large influence on relevant properties like thermal insulation, air, and water vapor permeability.
Clothing determines how much of the heat generated by the human body can be exchanged with the environment. This is very important because the human body will be in a state of comfort when the core body temperature is about 37°C and there is no perspiration on the skin surface. A heat balance between the heat produced by the human body with heat exchange between the body and the environment maintains the human body temperature. Overall thermal balance may be attained at numerous combinations of the thermal environmental parameters and outfit properties.
Our perception of comfort depends on such factors as weather conditions, levels of physical activity, the physical and physiological status of individuals, the properties of textile materials etc. During an extensive physical activity, body temperature increases with enhanced heat production, and the body will perspire in order to withdraw energy from the body by evaporation of sweat. What about different weather conditions?
In cold weather
Since only 10% of heat loss is related to respiration, in cold weather conditions, clothing plays a prominent role in maintaining the overall heat balance through thermal protection and insulation. Thermal insulation is one of the most important factors since it prevents cooling of the body parts and ensures that the body is warm enough. To provide enough thermal insulation, an outerwear must be:
- Breathable – When talking about clothing, perspiration permeability means that a garment can permit the passage of moisture through its surface. Some fabrics and garments are much more breathable than others. The degree of breathability is usually measured in terms of the amount of water vapor that can pass through a square meter of the material in 24 hours or g/m2. A fabric graded 5000g/m2 is slightly breathable, while one with 10 000g/m2 is considered breathable enough for moderate activity. If you need a waterproof breathable jacket for highly aerobic activity, check out those with a label 20 000g/m2.
- Waterproof - Waterproof outerwears guarantee that little or no moisture can permeate from the outside. At a hydrostatic pressure of 5000mm water column, a fabric is water-resistant and will protect you from light rain and dry snow. Fabric with a 10 000 to 15 000mm water column can withstand a moderate rain. A fabric with a hydrostatic pressure of 20 000mm or more is fully waterproof and will protect you in heavy rain and wet snow. For more information on this, check out our blog post about waterproof and water-resistant fabrics.
- Wind-resistant - Since they can handle wind gusts very well, windproof garments offer full protection from the wind meaning that you will experience no convective heat loss.
Waterproofness and breathability are contradictory requirements so a compromise between protection and comfort properties must be made. This trade-off between waterproofness and breathability is one of the most important things to remember regarding waterproof breathable jackets. It’s usually achieved by adapting the porosity and thickness of such waterproof breathable layers. Anyway, WBF have some limitations and can’t do wonders no matter how the manufacturers tout their properties. For example, during high-intensity activities, you sweat a lot and there’s no way that you stay dry regardless of your jacket’s features/characteristics. The same is also valid in a heavy rain or in very cold weather - then the thick clothing further reduces breathability.
In warm weather
The human body uses several mechanisms to stay comfortable in hot conditions. Heat loss through perspiration evaporation, and heat and water vapor flux through textiles are very important for the comfort of warm weather clothing. When the environmental temperature is greater than the skin temperature, your body responds by sweating in order to cool. Generally, perspiration evaporation through clothing is an extremely effective method for the removal of excess body heat. Thus, in such conditions, you need moisture-wicking and breathable clothing, which won’t leave you feeling hot and damp.
No, it's not a joke! Despite all the negative things you can read about this natural fabric, it is used in some of the most sophisticated insulated jackets and it works pretty well. Do you remember the first waterproof breathable fabric called Ventile (it is actually etaProof cotton that is presented under this brand)? Well, it is densely woven from 100% cotton and unlike other WBF it isn’t coated or laminated. Ventile has excellent weatherproofing properties due to the properties of the special long staple cotton fibers. When dry, they retain an open, breathable structure. When wet, they absorb water and swell to close fiber interstices, thus making the fabric impermeable to water. In addition, it’s also durable, quiet, windproof, and highly breathable material still used for military clothing as well as for clothing used for expeditions in extreme weather conditions. Well, not all garments made from this material are waterproof - the producer prefers using the term weatherproof. However, outerwears made with double layer Ventile provide excellent protection from cold, rain, and snow. They aren’t cheap, though. Just like other fabrics used in the production of waterproof breathable jackets, Ventile garments are impregnated with a durable water repellent (DWR) to additionally enhance the water-resistant properties of the fabric. So if you’re looking for 100% natural and environmentally friendly fabric… you won’t get it here.
Down from ducks and geese is the lightest and warmest natural insulation (used for producing premium sleeping bags too). Compared to synthetic fills, insulation jackets filled with down provide much more warmth for the same weight. Moreover, down is more durable than synthetic insulations and will outlast any synthetic fill. Additionally, it’s ultrapackable and very comfortable. Clearly, down has some disadvantages too. Firstly, it is expensive. Secondly, it is so warm that you cannot use it for high-intensity outdoor activities such as backpacking. And finally, down must be kept dry because it can absorb vast amounts of water and what’s worse - when sodden (it’s also susceptible to ambient humidity or trapped perspiration) it loses its insulating ability and dries slowly. The last argument is valid for pretty much all kinds of insulation - your insulated jacket should never get sodden, in general. The fill power (the spatial displacement for an ounce of down measured in cubic inches; for instance, one ounce of 850-fill power down will displace 850 cubic inches) differentiates different kinds of down. The higher the number, the warmer the down weight-for-weight. Down with 800-fill power or more is considered premium.
Synthetic insulations are less expensive and more reliable than down in wet and cold conditions. It is because synthetic insulations don’t absorb much moisture, dry quickly, and keep some of their warmth when damp. The best synthetic insulations are soft and comfortable and have good durability but they still won’t last as long as fleece or down. However, compared to down, they are less thermally efficient, less soft, less compact and won’t last as long as fleece or down as they do not recover fully from repeated compression. Just for a comparison - modern high-end synthetic insulations are warmer than fleece but not as warm as a high-end down. They are also much more compressible and wind-resistant than their cheaper counterparts.
Some insulated jackets are fleece lined. Fleece is warm, breathable, and relatively cheap, so when sandwiched between water- and windproof shell fabrics, it provides a very good thermal insulation. For more in-depth information about fleece, its pros, cons, and features, you can read our post dedicated to fleece fabrics.
Shell fabrics & features
Since both polyester and nylon are durable and hydrophobic, they’re the most widespread shell fabrics. Together with the type and amount of insulation, the shells used are the most important feature of insulated jackets because they affect both the weight and warmth of an outer layer. A shell fabric must have some air permeability so that water vapor can pass through it and evaporate into the atmosphere, though too much air permeability means that body heat will escape too easily. The shell fabric can also improve the water resistance of an insulating layer against precipitation or condensation. For this reason, it’s usually treated with a DWR.
Insulated jacket design
Material alone is not enough to ensure that a hardshell will perform well as design also matters. Design depends on the garment’s price as well as on the jacket’s function.
Cheap insulated jackets are manufactured from unspecified fabrics. Their features often include only a hood and hand pockets. More expensive jackets typically have more features and technical details (though some of them incorporate expensive branded fabrics and may not include many details) such as WBF, sealed seams, water-resistant zippers, underarm zippers etc. Among the most expensive harshells dominate Gore-Tex 3-layer laminates. These waterproof breathable jackets are aimed at more demanding activities like mountaineering where the users are exposed to extreme conditions and, thus, need some additional features like ergonomic cut, helmet compatible hoods, specially designed pocket and drawcord function. You can see such a design in the figure below.
Typical Waterproof Breathable Jacket Design
Source: High-Performance Apparel*
Features and details
- Size and length - An insulated jacket should be a size large enough to allow for additional layers of clothing underneath without restricting mobility. Length is a matter of personal choice. For example, hip-length garments give legs greater freedom of movement, while a length that extends well below the waistline of pants and a drawstring at the waist so the torso can be sealed off.
- Hood - An adjustable hood with a brim, neck flap, and good drawstrings will protect your head from wind and water. To ward off rain, hoods should fit closely around your face when the drawcords are tightened, without leaving a gap under the chin. Depending on the jacket’s purpose, hoods might have some additional specific features. If you want to look neat in town, a hood that rolls into the collar would be a convenient addition to the design. The same feature seems pointless in the backcountry or in the mountain where functionality is of prime importance. Detachable hoods are also more convenient for town use than for backcountry use since most are very difficult to attach while wearing the jacket. For people who wear glasses, features (like a wired peak or visor) that do not impair vision are essential. However, for most hoods, there’s a trade-off between protection and good vision as the hoods that limit vision most are often the ones that give the best protection.
- Adjustable openings - Found at the waist, hood, and cuffs. Drawcords are needed at the collar for tightening the hood. They are also often found at the waist. Cuffs need to be adjustable to offer a more precise wrist fit. Elastic-bound sleeve cuffs or Velcro-closed ones are a very useful addition to the jacket’s design. The main function of all adjustable openings is to keep the cold out and seal in warmth.
- Underarm vents - Underarm zippers are used for ventilation and can be handy when your exertion level rises. However, sometimes it’s hard to zip or unzip the vent during movement especially if your other hand is busy and you have to do it with one hand only. Waterproof breathable jackets often have such a feature.
- Zippers - Quality zippers are an important part of a good and functional outerwear. They are strong with large, durable teeth and good flaps that keep the zipper dry without restricting air circulation and ventilation.
- Seams - A potential leak point in any garment. That’s why having well-bonded, tape-sealed seams is so important. While in waterproof breathable jackets seams are usually taped, in cheaper garments, seams may not be taped.
- Pockets - Easily accessible pockets are another essential part of a quality insulated jacket. They might have covering flaps for added rain protection. Alternatively, they might just have water resistant zip closures. Pockets are useful for fitting items such as maps, compasses, hats, gloves, and other small items. There’s a variety of pockets in sizes, closures, materials, and location on the outerwear. Just to name some of them, your jacket might have chest pockets, hem pockets, inner pockets, wrist pockets, music pockets etc.
Typical Insulated Jacket Design
Source: High-Performance Apparel**
The main function of an insulated jacket is to keep you sufficiently protected from the elements. Hence, it must be windproof and waterproof. Waterproof breathable jackets are best since they ensure moisture transfer from your body to the environment, this way avoiding excessive sweat accumulation.
Thermal insulation is among the most important factors in cold weather conditions. To provide enough thermal insulation, an insulated jacket must be breathable, waterproof, and wind-resistant. No matter what manufacturers claim, keep in mind that as far as waterproof breathable jackets are concerned, there's always a trade-off between waterproofness and breathability.
Down, synthetics and cotton are among the most widely used materials for insulation and each one of them has its pros and cons. In addition to the material used, jacket design plays an important role for insulated jackets' appearance and functionality.
* In J. McLoughlin, & T. Sabir (Eds.), High-Performance Apparel: Materials, Development, and Applications, 2018, Elsevier Ltd., p.446
** In J. McLoughlin, & T. Sabir (Eds.), High-Performance Apparel: Materials, Development, and Applications, 2018, Elsevier Ltd., p.440