Tech: Down &
Synthetic Insulation

Down is the soft underlayer found beneath the outer feathers of geese and ducks. It consists of delicate clusters of fine filaments that radiate from a central point.

These clusters trap air – the true source of warmth. Air acts as an exceptionally efficient thermal barrier, unmatched by any other natural material. Because down is almost entirely composed of trapped air, down-filled garments are remarkably light, compressible and warm.

At The Mountain Studio, we use only RDS-certified down to ensure the highest standards of quality, traceability and animal welfare.

Down is the undercoating found beneath the exterior feathers of geese and ducks. It consists of clusters of light, fluffy filaments that grow from a central point.

These clusters of down trap air, and this air is actually what keeps you warm. Air is an incredibly efficient thermal barrier, unrivalled by any other material. The down’s volume is almost entirely filled with this trapped air, which makes down-filled garments both lightweight and compressible.

Baffles

Baffles are the compartments formed between two layers of fabric that keep the down evenly distributed throughout the garment.

Fill Power

Fill power, sometimes referred to as loft, measures the relative quality of down. It’s determined through a lab test that calculates how many cubic inches one ounce of down (just under 30 grams) can fill.

In general, a higher fill power indicates greater loft and more efficient insulation. While it gives an idea of a jacket’s potential warmth, other factors – such as the total amount of down used – also influence overall performance.

Down Cluster Ratio

This ratio shows the balance of down and feathers used in the insulation mix of a garment. A higher ratio means more down content, resulting in a better warmth-to-weight performance. For example, an 80:20 ratio means that no more than 20% of the filling is feathers.

RDS Down

The Responsible Down Standard (RDS) is an internationally recognised certification that ensures down and feathers are sourced from ducks and geese raised in accordance with strict animal welfare principles. To carry the RDS label, 100% of the down in a garment must come from certified sources.

Synthetic insulation is man-made, typically crafted from polyester in either sheet or lofted forms that mimic the structure and warmth of down. Fine filaments of varying sizes create air pockets that trap heat and provide effective protection against the cold.

Durable yet lightweight, synthetic insulation dries quickly and retains warmth even when damp, making it ideal for high-intensity activities or wet conditions. When paired with breathable fabrics, it adapts to your activity level, offering insulation or ventilation as needed to help regulate body temperature in changing environments.

Primaloft

PrimaLoft® is a water-resistant synthetic insulation that offers warmth and protection comparable to down, even in harsh conditions. It’s made from fine polyester microfibres that create small air pockets to trap body heat and retain warmth.

PrimaLoft® Gold is the highest-performing version, combining low weight, water resistance and quick-drying properties – making it an ideal choice for demanding conditions.

G-Loft

Developed by the Austrian company Goldeck Textil, G-Loft® is a synthetic insulation made in Europe, known for its excellent warmth-to-weight performance.

G-Loft® Eco EVOX is made from recycled polyester and designed for lightweight, breathable warmth. It stays warm when wet, dries quickly, and combines the loft of down with the durability of synthetic fibres – ideal for active mountain wear and ski clothing.