Synthetic Insulation Explained

Posted by Mark Richardson on Feb 10, 2020

Synthetic Insulation

We look at the three types of synthetic insulation and other factors to consider when choosing your synthetic garments

Understanding Synthetic Insulation

There has long been a question over which is the best form of insulation for outdoor clothing; synthetic or down? Traditionally, if you were heading somewhere wet you would be better served with the heavier and bulkier synthetic jacket as it stayed warm when wet. Down was ideal for cold, dry conditions where weight and pack size were more of an issue.


However, the gap between the two has been narrowing for some time with the use of hydrophobic down making it more weather resistant while advancements in technology have enabled synthetic materials to more closely mimic down with significantly lower weights and pack sizes.

Types of Synthetic Insulation

Synthetic insulation can be placed into three general categories. These categories provide different benefits and are aimed at different users. The traditional synthetic material was a simple mat structure, a roll of material that provides weather resistant warmth.


The loose-fill approach has seen huge advancements in recent years as technological advancements have allowed this to more closely mimic the properties and performance of down. Finally, there is active insulation which provides warmth but is focused on delivering excellent breathability, wicking and moisture management for use in active outdoor pursuits.

Mat Structure

Led by Primaloft synthetic 'mat' insulation provides outstanding warmth for weight, is durable and is largely unaffected by wet conditions. Traditionally this type of insulation is not very breathable leading to clamminess during periods of high activity.

Highly Breathable

Polartec are leading the way with their 'Alpha' insulation. Weight for weight it only offers about half the insulation of synthetic mat insulations but it offers much greater breathability and will transport moisture out of the garment. A property which is ideal for keeping warm during high activity.


Loose Fill

Loose Fill, 'Down-like' - The latest synthetic fillings mimic down by providing high levels of insulation (the equivalent of around 600 Fill Power Down), high loft and compressibility along with superior wet weather performance and is non allergenic.



The simplest way of understanding the warmth of a synthetic jacket is to look at the weight of the insulation. This is normally shown in grams per square metre.


For active insulation and versatile, mid-weight insulation you would expect between 50-150g/sqm of fill. This is still quite a broad range which allows you choices as to how much warmth you need in your active insulation jacket or how light and packable you want an all-round jacket to be.


A jacket for static warmth where weight is not an issue would generally use well in excess of 150g/sqm of insulation. Since warmth is more important than weight saving the fill weight can rise well above 200g/sqm and be combined with denser, more weather resistant outer fabrics too.

Additional Features

Being realistic about what you will use the jacket for most of the time is important for making the best choice. Which features are vital and which are luxurious? Understanding your needs will help you choose the best one.


Hood Adjustability
Firstly, whether or not you need a hood is down to personal preference and whether you will be using the jacket as a midlayer or an outer layer. If the jacket will be used as a midlayer, under a shell, a hood may not be needed because it could result in 'hood overload' if additional layers are going to be worn over the top of it. However, if this is going to be an outer layer and a hood is required, how technical and adjustable do you need it to be? Is the hood going under, over or be used without a helmet?


Pocket Placement
Pocket placement is important depending on your activities. If you are going to be climbing or hiking with your jacket then higher pockets are beneficial as the harness or hipbelt can obstruct access. Higher pockets or chest pockets only allow you to keep more kit close to hand. Lightweight jackets may be limited to just one small chest pocket that doubles as a stuff sack so it is always worth noting how many pockets there are compared what you need.


Along with the developments in recreating the properties of down, synthetic insulation has seen a focus on improvements surrounding the environmental aspects of it's production and use. From ensuring bluesign production throughout to increasing the amount of recycled content while still improving performance.

There are three main types of synthetic insulation and we discuss them here and give other advbice on choosing sythetic garments.