PMO / Fabric Exploration
Not all insulation is designed to retain as much heat as possible. When moving through changing conditions, the challenge is often finding the balance between warmth, breathability and comfort.
Developed by Polartec® and originally engineered for US Special Operations Forces, Alpha® introduced a different approach to insulation, one built to perform during periods of both high exertion and rest.
Lightweight, highly breathable and fast drying, its distinctive construction has made it a widely adopted material within modern outdoor clothing.
But how does it work? What makes it different from traditional fleece? And how should it be worn?
We answer 12 of the most frequently asked questions about Polartec® Alpha®.
01 What is Polartec® Alpha®?
Polartec® Alpha® is a synthetic active insulation technology designed to provide warmth while allowing excess heat and moisture to escape.
Unlike conventional insulation, which primarily focuses on retaining warmth, Alpha® uses an open structure of lofted fibres attached to a knitted mesh core. This construction allows air to move through the material, helping regulate temperature during physical activity.
The result is lightweight insulation designed for environments where conditions and activity levels are constantly changing.
02 What is active insulation?
Active insulation is designed to balance warmth and breathability during movement.
Traditional insulation, such as down or synthetic fill, is generally focused on retaining body heat. While highly effective in cold conditions, these materials can become uncomfortable during strenuous activity when the body generates excess warmth and moisture.
Active insulation addresses this by allowing greater airflow through the material, helping reduce overheating without sacrificing insulation entirely.
It is particularly useful for activities involving frequent changes in intensity.
03 How does Polartec® Alpha® work?
The technology relies on a combination of lofted synthetic fibres and an open knitted structure.
The lofted fibres create air pockets that help retain warmth, while the mesh core allows air and moisture vapour to move through the material.
Rather than physically adjusting its structure in response to temperature, Alpha® provides continuous air permeability. As the wearer moves, changes in airflow and body heat influence how much warmth is retained or released.
This balance between insulation and ventilation is what makes Alpha® particularly effective during stop-start activities.
04 What is the difference between Polartec® Alpha® and Alpha® Direct?
Both technologies use the same fundamental approach to active insulation, but differ in their construction and application.
Original Polartec® Alpha® was developed as an insulating material that could be incorporated between outer and inner fabrics.
Alpha® Direct uses a refined fibre construction that allows the insulation to be worn directly against the skin or another garment, without requiring an additional lining.
Removing this extra fabric can reduce weight, increase breathability and improve drying times.
Alpha® Direct also exposes the material's distinctive lofted texture, giving it a recognisable appearance.
05 Is Polartec® Alpha® warmer than traditional fleece?
Not necessarily. The key difference is how warmth is managed.
Traditional fleece provides dependable insulation and can offer greater warmth in heavier constructions. Polartec® Alpha®, however, is engineered to balance insulation with increased airflow.
During physical activity, this can make Alpha® more comfortable by allowing excess body heat to escape.
For low-output activities or extended periods of rest, a thicker fleece or more protective insulated jacket may provide better warmth.
The choice depends on the intended use, fabric weight and surrounding conditions.
06 What do Polartec® Alpha® 60, 90 and 120 mean?
The numbers commonly associated with Alpha® fabrics refer to their approximate fabric weight, expressed in grams per square metre (gsm).
- 60gsm: A lighter construction prioritising minimal weight, breathability and packability.
- 90gsm: A versatile middleweight option balancing warmth and airflow.
- 120gsm: A heavier construction offering increased insulation for cooler conditions.
Higher fabric weights generally provide greater warmth, but they can also increase weight and bulk.
These numbers are useful when comparing fabrics, although actual performance also depends on garment construction, fit and layering.
07 Is Polartec® Alpha® windproof or waterproof?
No. Polartec® Alpha® is an insulation technology, not a waterproof or windproof membrane.
Its open structure is designed to encourage airflow, which is beneficial during high-output activity but means that exposed Alpha® fabrics provide limited protection against wind.
In colder or more exposed environments, combining Alpha® with a wind-resistant or waterproof outer shell helps retain warmth while providing additional weather protection.
This makes it particularly effective within a considered layering system.
08 Can Polartec® Alpha® be worn directly against the skin?
Yes, although this depends on the specific construction.
Polartec® Alpha® Direct was developed to allow the insulating fibres to sit directly against the skin or other clothing layers without requiring a separate lining.
It can function as a lightweight insulating layer worn over a base layer or, where the garment is designed for it, directly against the body.
When paired with an outer shell, its open construction can provide breathable warmth while the outer layer controls exposure to wind and rain.
09 Does Polartec® Alpha® keep you warm when wet?
Polartec® Alpha® uses hydrophobic synthetic fibres that absorb relatively little moisture and are designed to dry quickly.
Its open construction also encourages moisture vapour to escape, helping manage perspiration during sustained movement.
Unlike down, which can lose significant insulating performance when saturated, Alpha® can continue to provide useful insulation in damp conditions.
However, it is not waterproof. In prolonged rain or severe weather, a suitable protective outer layer remains essential.
10 What activities is Polartec® Alpha® best suited to?
Polartec® Alpha® is particularly suited to activities that involve changing levels of exertion.
Trail running, hiking, climbing, cycling, mountaineering and ski touring can all benefit from lightweight insulation that allows excess heat to escape during movement.
Its low weight and compressibility also make it useful for travel and everyday layering.
The defining advantage is versatility: providing insulation during cooler periods while remaining breathable enough for more demanding activity.
11 How do you wash and care for Polartec® Alpha®?
Proper care helps maintain the material's loft, structure and performance.
Gentle washing with a mild detergent and avoiding fabric softeners can help preserve the material. Always follow the garment's individual care label, as instructions vary depending on construction and additional materials used.
Exposed Alpha® Direct fabrics should also be handled carefully to minimise snagging and unnecessary abrasion.
With appropriate care, Alpha® is designed to retain its insulation and breathable properties through repeated use.
12 Why is Polartec® Alpha® important to modern technical clothing?
Polartec® Alpha® represents a shift in how insulation is approached.
Rather than prioritising warmth alone, the technology considers how the body generates and releases heat during movement.
Its development has expanded the possibilities for technical garment design, from breathable insulated jackets to lightweight, exposed-fibre midlayers.
For Purple Mountain Observatory, Alpha® demonstrates how material innovation can improve the relationship between clothing, the wearer and their environment.
Through our continued exploration of Polartec® technologies, including Alpha® Direct and Alpha® Wool, we are interested in how these developments can shape the next generation of technical apparel.