Synthetic insulation is widely used in outdoor jackets as an alternative to down. This guide explains how more sustainable synthetic insulation jackets are made, how they compare to natural materials, and which factors influence their environmental impact.

Outdoor jackets with synthetic insulation provide warmth and durability without using animal-derived materials. This buyer’s guide explains how synthetic fibre fillings are produced, how they compare to down, which alternatives exist, and what factors influence their environmental impact.

When choosing a warm winter jacket, buyers often weigh down insulation against synthetic alternatives. Both materials have functional advantages and environmental trade-offs.

Down is widely used in jackets and sleeping bags because it offers high warmth with low weight and good compressibility. However, when down becomes wet, the feathers can clump together and lose insulating performance. Some down products are treated to repel moisture, but these treatments can involve substances such as per- and polyfluoroalkyl substances, also known as PFAS. Jackets insulated with down are often more expensive than comparable products with synthetic fillings. Animal welfare considerations may also influence purchasing decisions, as the conditions under which geese and ducks are raised vary widely.

Synthetic insulation jackets compared to down

Synthetic insulation is typically made from polyester fibres. Compared with down, these materials are generally easier to care for and retain their insulating properties when wet. Jackets with synthetic insulation are often less expensive and more resistant to moisture.

Several types of synthetic fibre fillings are commonly used in outdoor clothing, including Primaloft, Polarloft, and Thinsulate.

Common synthetic insulation materials

Primaloft is made from fine polyester microfibres designed to mimic the structure of down. Small air pockets within the material trap body heat while limiting heat loss. The insulation is compressible, water-repellent, and designed for durability. Primaloft is available in multiple variants, including versions with different insulation performance levels, reduced-emissions manufacturing processes, biodegradable fibres, and recycled content derived from post-consumer materials.

Polarloft is a synthetic insulation used primarily by Mountain Equipment. It is designed to offer warmth at relatively low weight, retain thermal performance when wet, and allow moisture to pass through the material. Variants include blown-in insulation that resembles the construction of down jackets, as well as versions developed to prioritize breathability over insulation, which are often used in mid-layers.

Thinsulate consists of synthetic microfibres that are finer than down. The dense fibre structure allows the material to trap air efficiently, contributing to thermal performance. Depending on the version, the fibres are made from polyester or a blend of polyester and polypropylene. The insulation is designed to be breathable and moisture-repellent.

Environmental impacts of polyester insulation

Polyester is widely used in textiles because it is durable, lightweight, and quick-drying. In 2015, approximately 65 percent of all textile fibres produced globally were synthetic, with polyester accounting for the majority. Polyester is used not only in clothing but also in footwear, accessories, and home textiles. Because it is derived from fossil fuels, its production and disposal contribute to environmental impacts. In 2015, an estimated 98 million tonnes of oil were used to produce polyester.

Bio-based polyester made from renewable raw materials such as sugarcane is available, but its use remains limited. Some studies have found that bio-based polyester can have a similar or slightly higher carbon footprint than fossil-based polyester, due to agricultural inputs and energy-intensive processing. Bio-based polyester is also not necessarily biodegradable.

rPET and microplastics

Recycled polyester (or rPET) generally has a lower carbon footprint than newly produced polyester. While textile-to-textile recycling facilities are under development, most recycled polyester currently used in clothing comes from PET bottles rather than discarded garments. Using PET bottles for textiles interrupts an existing closed-loop recycling system for bottles, and only a small proportion of textiles are currently recycled into new clothing.

Another environmental concern associated with polyester is the release of microplastics through abrasion during washing and wear. Microplastics have been detected widely in the environment and in human tissues. Research into their health effects is ongoing. To reduce fibre shedding, garments can be washed less frequently, aired out between uses, and washed in full loads.

Bio-based alternative insulations

For those seeking alternatives to synthetic insulation, several natural filling materials are available. Down remains the most common option. Wool-based insulation is also increasingly used in outdoor clothing.

Virgin wool is often sourced from sheep raised for meat production and is therefore considered a byproduct. Wool fibres create air pockets that retain heat while allowing moisture regulation. Wool insulation can provide warmth even when damp and has natural odor-resistant properties. In outdoor applications, wool is frequently blended with other fibres, including polyester, polylactide, down, or silk.

Lavalan is a fibre blend made from European wool and corn-based polylactide. The material is designed to be breathable and moisture-regulating.

Silkwool is a blend of silk, wool, and plant-based polylactide. Silk supports moisture transport, while wool contributes insulation and temperature regulation.

Kapok is a plant-based fibre obtained from the seed pods of the kapok tree. The hollow fibres are sometimes described as a down alternative due to their loft and light weight.

Choosing lower-impact synthetic insulation jackets

Several general considerations can help reduce the environmental impact of insulated jackets. Durability and long product lifespans can reduce the need for frequent replacement. Avoiding problematic chemical treatments, choosing materials that are easier to recycle, maintaining and repairing garments, and extending use through resale or second-hand purchasing can also reduce overall impacts.

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