Men's Siege Technical Fleeces

Our lightweight men's mid-layers and men's fleece jackets are ideal for hiking, mountaineering, skiing and trail running in colder climates and winter conditions. Indeed, we've worn the Siege men's tech fleece and men's insulated clothing during thru-hikes on the Isle of Skye, climbing in Wales and even whilst skiing in backcountry Japan.

The construction of Polartec® Power Grid™ differs from conventional fleece owing to its grid like structure. Rather than blanket you in a solid wall of fleece, Power Grid™ has tiny air channels that criss cross its surface giving the fabric its name. These air channels enhance the Siege Tech Fleece's moisture wicking and breathability compared to conventional fleece. That means you stay insulated on the approach and don't overheat on the climb.The construction also reduces overall weight compared to a traditional fleece at equivalent warmth, making it the right choice when you need a mid layer that works as hard as you do. That is why we chose it for the Siege collection.

The Siege Tech Fleece is built for those who are on the move constantly, that's why we've worn it for multi-day hikes in the British isles, Alpine traverses and even our summit of Ama Dablam. The Power Grid™ construction manages heat and moisture dynamically, trapping warmth during lower-intensity moments and venting effectively when your output increases. This means you avoid the overheating and damp chill cycle that undermines cheaper fleeces on demanding pursuits. It layers cleanly under a hardshell without bulk, and the lightweight construction reduces fatigue on long days in the mountains. For hiking, mountaineering, trail running, and ski touring it is the mid layer of choice when breathability cannot be compromised.

In dry, cool conditions with low wind the Siege Tech Fleece can be worn as a standalone outer layer, for example on a sheltered climb or a low-exposure trail. However, fleece fabric is not inherently wind or waterproof, and in sustained wind or rain it will not provide adequate protection on its own. For anything beyond mild, settled conditions we recommend layering the Siege under a waterproof hardshell or softshell. The Power Grid™ construction is specifically optimised for use as a mid layer to be paired with shell jacket or insulated jacket.

The Siege and Mantra sit at opposite ends of our fleece range. The Siege Tech Fleece is built for movement: lightweight, highly breathable Polartec® Power Grid™ construction designed for high-output pursuits where managing heat and moisture during activity is the priority. The Mantra Fleece is built for warmth: a lofted Polartec® Thermal Pro® pile designed for lower-output or static conditions where staying warm when you stop moving matters most. If you run hot and move fast, start with the Siege. If you are belaying, stationary at altitude, or heading into serious cold, the Mantra is the one to reach for.