Alpha Direct bags are built with only a fabric shell
Climashield Apex is built with both fabric shell and liner
Our limited usage with Alpha overbags have ranged from 35°F to 10°F in both dry and snowy environments; and mostly cowboy camping. Apex have seen similar conditions, but many more nights over a much longer period.
Both materials are very effective keeping the underlying down dry and fluffy, with condensation forming only inside (low CFM) or outside the shell fabric.
Alpha (4004 only)
For best performance with this minimum loft insulator the shell fabric should be a very low CFM material to entrap warmth. An 8-10°F boost is then a reasonable guess.
Without an inner fabric these bags transmits expelled body vapor readily through the Alpha. On the flip side, there is more friction in use and small debris can get caught in the fleece. The first is only noticeable when using the bag directly against base layers; and the former is not showing much accumulation so far.
While on paper the 4004 is the same weight as 2.5 Apex, in real life the Alpha is heavier. I could be wrong, but I attribute this partly to the very consistent weave of the Alpha compared to the uneven density of Apex, almost mirroring that of loose fill insulation. The result is a near identical finished weight between the dual layer Alpha and triple layer Apex bags.
This airy fleece like material seems durable and maintains a consistent ‘loft’ after use. It recovers well after compression.
It suffers from the inevitable shedding of micro fibers. Apex breaks down like this too, but the fallout is contained between layers of fabric.
Alpha is very compact in one’s backpack. It folds and rolls like a pair of pants. In addition we feel applying relatively heavy compression comes with few consequences.
Apex (2.5 only)
Due to the slightly taller loft one can use a high CFM shell fabric with good results, but lower air permeability materials will again increase warmth. Expect a gain of 15°F when new.
This mono filament material has a traditional lay up that entraps air readily, but also makes it more fragile. Loft decrease is real. The use of thinner Apex (2.5 and less) makes the degradation less extreme and possibly extends the expected performance.
Since the Apex is fully enclosed, monitoring its condition is difficult.
Data for Apex has been collected for years. It’s a predictable product with known pros and cons.