The pack is 60L* expanding verticall to 100L*.
The pack expands vertically and the lid 'floats' on the closure straps which is attached to the pack with press studs - because of this it can be easily removed if you use it as a duffle.
There is one internal pouch and one external pocket - the internal pouch is, I think, designed to hold extra padding (kip mat folded flat etc) against your back. This internal pouch has no top closure and is, in the 60L mode, hidden by the vetical expansion tube. The external pocket is the lid, it's reasonably spacey - I keep losing stuff in it

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The main compartment is cinched up with a cord at both capacities. Because of the way in which it closes up there is a definate need for the use of dry bags.
Even with no frame and unpaddded straps, I find the pack to be quite comfortable to carry.
The padding on the back is contained in a rubberised material and activity will cause sweaty back syndrome by the bucket load.
As with a lot of packs of this type there is no shoulder strap adjustment when it's worn. Donning the pack is eased by a snap and ring affair on the left strap, the pack is slung over the right shoulder first and then the left strap is reassembled.
Oh, and the waist belt ...

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I quite like it

but I'm considering changing up to something that can accomodate Roomdolf.
* approximately