Part of the Berghaus Extrem range of technical clothing and equipment, the Power Stretch Full Zip Jacket uses Polartec's excellent stretchy fleece and is intended to work primarily as a close-fitting, efficient, insulation top worn under a weather-resistant shell layer.
The fact that Power Stretch has been around so long and not been messed with tells you something straight away - if it ain't broke, don't fix it. The fabric gets stretch courtesy of a 13% elastane content and warmth and wicking from the remaining 87% which is polyester fleece. The inner is fleecy and the outer is smooth for better wear resistance.
The pros of Power Stretch are that while it gives around the same level of warmth as a microfleece, the stretch means that it can cut to fit closer without being restrictive, which means it insulates more efficiently and sits more neatly under close-cut shell layers.
For us, Power Stretch is bang on for active winter insulation worn under a shell. Warm enough to keep you comfortable on the move but no so warm that you overheat easily. The Berghaus jacket is a nice medium length for some extra protection and a close, but not tight fit and twin zipped hand-warmer pockets give some storage if you feel you need it.
Over the recent mini ice age, this and a couple of other Power Stretch tops, did sterling work and were in more or less constant use. Wicking and breathability are both good too when things do get warm. If you run on the cold side, you may need something warmer, but for hot-blooded to 'normal' types, we think PS is spot on most of the time.
As far as the specifics of the Berghaus jacket go, stretchy fabric-bound cuffs and hem both sealed neatly and the double thickness collar is close fitting enough to form an effective neck seal. If you were being hyper-critical, the shoulder seams could be off-set further away from the point of the shoulder, though we didn't have any issues with chaffing from pack straps, so maybe that's a little picky.
Simple and effective design using a killer fabric that's still our number one choice for active cold weather layering use. It insulates 'enough', breathes decently, wicks well and at 330g is light enough to chuck in your pack without noticing. Our only quibble is that you could buy a hooded and thumb-looped jacket made from the same fabric for around the same price from other brands.