I'm used to light rucksacks, even for backpacking, and I know you can get a good 60 litre pack with internal frame and a comfortable carry around the 1kg mark (Granite Gear's Crown VC and Exped Lightning 60 are our favourite examples), so the Boreas is a bit heavier than this at 1.32Kg - the question is what do you get extra for the extra weight. In this case the answer is pretty simple - the weight of the pack seems to be in the harness system, which is very good indeed. The frame is a sheet format with thickly ridged foam contained within a mesh back panel - its very rigid, which helps transfer the load to the hips very well. The hipbelt is substantial and well padded - so, what the Buttermilks 55 offers over lighter packs of this capacity is additional comfort - the few hundred grams difference gives you a choice - the comfort of the Buttermilks is in the same category as Granite Gear's Blaze series.
As a comfortable backpacking rucksack then, the Buttermilks nails it. I feel the capacity is good as well, some packs may say they are 55 litres but they seem to be very small, in this case though I think the main compartment must be 55 litres in itself as I had no trouble getting all my gear in plus 6 days food. Total weight at the beginning of the trek was just below 30lbs (13.6Kg). There's also something about the proportions of the pack that's very good, I think it must be wider across the back because despite its 55 litres the load sits close to your back and not very high - in fact it sits right where you want it.
The hipbelt pockets are stretch mesh and are quite large and easy to get in and out of. The main compartment is flanked by two stretch mesh pockets and there's also a big one on the front. These were great for storing the items I wanted during the day but are not accessible unless you take the pack off, this is because the top opening of the side pockets is quite high and you can't get your arm back and high enough. When wet I stored the flysheet in the large pocket, which was ideal for the purpose. There are 'daisy chain' webbing loops on the front of the pack which are neatly hidden away until required for something.
There's a flat zipped pocket at the top of the pack which I found ideal to take cash, documents, phone, electronics etc (protected by LokSaks of course). Inside the pack has a bladder pocket with tube exit port. The only negative I found was the top closure - its a drawstring affair but unlike other packs we like, which have a water resistant rolltop, the Buttermilks is just a simple drawstring with a small triangular flap that clips over to cover the hole. This looks vulnerable to us, in fairness the Buttermilks comes with a waterproof pack cover and with one in place I walked a full day in the rain and the pack was bone dry under it, so is it really a worry?
I tested the 55 Litre version - all the Boreas packs we stock share the same harness system so this review is relevant to them all, however the Buttermilks 55 Litre is the key pack for us as it is not much heavier than its competitors - when you look at the Buttermilks 40, its a heavy pack for 40 Litres. The Lost Coast packs have a more conventional lid, but again this adds weight, making the difference between these and other lightweight packs quite significant. Although you can be sure with all the Boreas packs that they will carry really well.