In reply to Daniel Heath:
it seems to me that primaloft has a "fluffy" less dense layer where it has frayed away from the main matting. the new rab gear leaves room for that, rather than just leaving room for the thickness of the primaloft as it comes.
so you actually get more loft for the same amount of primaloft. this, with the two layers of windproof pertex make it warmer than it should be for the amount of primaloft they put in.
hence the bin bag look.
the elasticated waist, together with the wrists, also helps to trap a warm layer of air underneath, aswell as within the jacket.
obviously though, if this is just for strutting round town in slim euro cut gear that hides your belly, it might not be the best option...