What Is An Insulated Jacket?

When planning a cold weather expedition, few considerations should be more important than your choice of insulation. Prolonged exposure to cold temperatures will drain the energy stored by your body and in extreme cases can lead to complications like hypothermia.

This guide to insulated jackets will tell you everything you need to know in order to best guarantee the safety and success of your trips this Winter and beyond.

How Do Insulated Jackets Work?

Insulated jackets do not work by generating heat but by trapping the heat generated by your body. Such a jacket will typically comprise of a water-resistant and/or rip-stop outer layer with insulation then stuffed within box compartments or “baffles” between the outer and inner layers. This insulation is usually made up of either “down” or “synthetic” fill, which we will explore in further detail later in this article.

An insulated jacket tends to be worn as part of a layering system. In extreme conditions this can mean up to 2 or three 3 layers in total once a base layer and fleece mid layer are included. In this instance, the insulated jacket provides a final windproof and water-resistant barrier against the cold. For milder conditions, an insulated jacket can simply be layered over a t-shirt to give the same effect.

Many ThruDark insulated jackets feature a Pertex® Quantum Pro outer layer. This is an ultra thin, rip-stop and water resistant coating that provides maximum durability and weather resistance at a relatively light carry burden. Its high level of water repellency is key in preventing your down or synthetic insulation from wetting out in damp environments (damp insulation generally performs less well).

Types of Insulation

ThruDark’s range of high performance insulated jackets use both down and synthetic insulation respectively in order to best offer you different options depending on your operational environment. 

Down Insulation

Down insulation features in our End of Days Parka, Breach, Patriot, Recoil and Melee Jackets in order to provide maximum insulation for extreme cold, dry environments. Down is most commonly sourced from ducks or geese and refers to the finest breast fibres on the bird, these being the lightest, loftiest and best insulating (as they are naturally designed to keep the bird’s vital organs warm).

At ThruDark, we traditionally use only the finest goose down from a responsible source. This down works by trapping warm air generated by the body between its lofted structures and this minimises loss of body heat and helps maintain a regular body temperature.

Down is routinely measured by “fill” or “fill power” i.e. the amount of down inside the jacket. It is important to note that fill power is measured by volume and not weight, the greater the volume, the higher the fill power. The higher the fill power, the better the jacket is at insulating. This is because it is those longer, more lofted structures that occupy more volume and trap more heat.

ThruDark insulated jackets range from 750 - 850 down fill (with 550+ down fill commonly considered to be a “good” standard of insulation by industry standards).

Synthetic insulation

Synthetic insulation has been chosen carefully for our Engage and Ithax Jackets as a more versatile offering designed for cold, damp environments. The reason being is that, unlike down, synthetic insulation maintains its insulating power in wet and humid conditions and will dry faster when wet. This is because synthetic fibres do not absorb moisture and so will not lose any loft as a result.

Synthetic insulation is made from polyester and is designed specifically to mimic the performance of down. However, synthetic insulation does not compress as well as down meaning you need more of it to achieve the same level of insulation. This can sometimes make synthetic insulated jackets bulkier and heavier. On the other hand, owing to its man-made structure, synthetic insulation is much less likely to shed than down thus making it a more durable, long term alternative in some instances.

For synthetic insulation, we use PrimaLoft® Gold Insulation Active+, a 55% post-consumer recycled polyester. The unique fibre structure of Primaloft® Gold Insulation Active+ prevents microfibres from migrating and hindering breathability. It allows excess moisture to escape through our Pertex shells which helps improve thermal regulation and overall comfort during dynamic performance.

 For added weatherproofing, PrimaLoft® insulation is also treated with a water-repellent finish to ensure maximum insulation even when wet.

Are insulated jackets waterproof?

Insulated jackets should not be confused with waterproof jackets as the two features are not widely combined.

Insulated jackets require a greater degree of breathability in order to prevent overheating and discomfort during performance. On the other hand, waterproof jackets operate with a lesser degree of breathability in order to minimise water ingress during wet weather. Waterproof jackets also typically feature a hard shell, making them less packable than a conventional insulated jacket.

In our case, all ThruDark insulated jackets are water resistant rather than waterproof, with the exception of our End Of Days Parka (which is both highly waterproof and highly insulated). Otherwise, the main bulk of our insulated jacket offering is constructed from a water resistant Pertex outer layer and finished with additional water repellent.

Water will bead for a short time during a shower but it is not advisable to wear down in the rain. For the reasons given above, if operating in cold but wet conditions, a synthetic insulated jacket such as our Engage Jacket should be worn. Failing this, it is advised to throw a lightweight waterproof over your down jacket in wet weather where applicable.

Which insulated jacket is right for me?

The primary thing to consider is whether you will be using the insulated jacket in cold/dry or cold/wet conditions as this will influence whether you opt for down or synthetic insulation.

You will then need to think about what temperature you will be using the jacket in - for the most extreme conditions you will want a high fill power (over 550+). In milder climes, a lighter jacket with a lower fill power may be more appropriate.

It is worth bearing in mind the packability of your jacket. Depending on the task at hand you may need to pack a lighter insulated jacket that stuffs down well into a daysack, for more short term or stationary pursuits you will likely get away with a heavier jacket that isn’t required to pack down.

None of these considerations should be made in isolation and the process is less a step by step one than an evaluation in the round. When preparing for an expedition you should be balancing the ideas of wetness, temperature and carry burden - depending on your particular pursuit you may need to compromise on one over the other.