In reply to blackreaver:
> I'm in a similar situation to the OP. I'm heading to the Alps for the first half of September and I'm looking for a lightweight bag.
> On the PHD sale section, they have a Minim 300 and a Minim 500 with water resistant outer coatings.
> Will the 300 version be warm enough for alpine bivys?
Depends on you, weather and altitude but that's what we use for alpine bivis, in fact the PHD photo (A bivvy in the Vallee Blanche) on the following link is my photo!
See
http://www.phdesigns.co.uk/product_info.php?cat=60&products_id=31
It packs small and weighs less than half a litre of water (465 grams) and despite PHD's conservative temperature rating we've happily used it bivving at well below zero wearing an extra layer or belay jacket.