I like Montane and, as a clothing manufacturer, they're certainly my preferred choice. However, having recently purchased a Lite Speed and the Nano Puff, I wondered where the Prism would fit in my current set-up. The combination of the Lite Speed & the Nano Puff, with a fleece hat, weighs only a little more (481g) than the Prism (mine is 414g) but gives me more versatility in terms of using either insulating layer and/or windshirt. The Lite Speed works well with my Montane Bionic base layer when I require wind protection (to prevent convective heat loss) but not protection from radiative heat loss (ie an insulating layer). The Prism does both jobs at once which can be useful, for example as a late/early 3 season, colder temperature option, but is potentially restrictive at warmer temperatures. However, the synthesis of primaloft & Pertex microlight is a distinctly breathable marriage so the range in which the Prism will be effective is broad. It obviously breathes better than two garments, as there would be, with two garments, at least another layer of Pertex for perspiration to travel through. It was always going be interesting to see how it performed when I would have used only the Lite Speed and the height & barren flats of the top of the Carneddau would be perfect.
There's no doubting the quality of the Prism. It's extremely well manufactured. Every detail is well-thought out & superbly crafted. I am a 33-34" waist, 20" torso, 39" chest & slightly broad shouldered. The medium fits me perfectly. The athletic cut means 90% range of unrestricted arm movement without the jacket riding up & that last 10%, arms above my head, results in limited movement of the hem, which has a two, one-hand drawcord toggles. Yet this does not make the jacket feel baggy at all. Full marks, therefore, for fit. I initially tried it on without a top & it felt pleasant enough against the skin so arms will likely not suffer from clamminess if a short sleeve base layer is worn. It is 40g primaloft fill with a Pertex microlight shell. Breathable, water resistant, very efficient insulating properties & it packs into one of the pockets to a 20x10x6cm parcel. There is a great post by Section Hiker on the principle of 'compactness' as an extension of lightweight principles that insulating layers, as opposed to fleeces or softshells, fulfil well. Even with a padded, adjustable hood, with velcro adjusters at the back which also help roll the hood away, or to tighten the adjustment, this packs down small and could easily be compressed further.
The pockets are padded with primaloft too which increases the protection from radiative and convective heat loss at the hands. There has been criticism of the wire brim to the hood - I think this is unjustified. It's malleable and useful. The interior zip flap is Montane's usual high-quality offering, which I like, and there is beardguard which the Nano Puff does not have. Both those mean it surpasses the Nano Puff. It feels more robust too - I could have a UL rucksack on the Prism without fear of degradation of the Pertex outer. I first put the Prism on when we stopped for lunch at the top of Pen yr Ole Wen and the wind was causing us real problems. It had a fairly instantaneous effect.
For those who do not know, Pertex MicroLight is a 30 denier microfibre nylon which, as a consequence of extremely tightly woven microfilament yarns, is highly windproof and manufactured to provide an effective barrier against down leakage. The fabric's tight weave enhances insulation by trapping more air so the loft of the insulating material is maximised (although a recent article on BPL would suggest loft does not necessary equal warmth). It is also constructed using DWR+ (a durable water-repellent treatment) which envelops each micro filament of the fabric with a hydrophobic polymer. This method of treatment gives remarkable water resistance which remains effective after washing but which does not impair breathability as is not a continuous coating. Where most nylon fabrics wick moisture directly through the weave, Pertex instead spreads it over a broad area by capillary action. Thus, moisture evaporates more readily. In the Carneddau, when surrounded by the damp mist within the clouds, and the wind battered us like a siege engine, I felt snug and protected. The Prism kept me warm when needed but breathed superbly as we moved fast to get below the cloud line for our camp. It is a great piece of kit.
In the warmer months, when wind chill will be more of a concern whilst moving than air temperature, I think the Lite Speed/Nano Puff combination might be preferable simply because the Lite Speed could be used alone, but as the weather gets cooler, the Prism surpasses that combination. It is very much a piece of kit I will look forward to testing in the winter months. It kept me safe in the Carneddau when the weather was anything but.