LowePro conspicuously underrate this product. The light, burly fabric appears as waterproof as any rubberised yellow outfit that a gnarly old fisherman would wear, and the roll-top design should keep the contents as dry as any submersible drybag on the market.
Yet LowePro very cautiously label the Dryzone BP 40l "splashproof". Indeed it only gets an official IPX-6 rating - which by internationally recognised standards, means 'water-resistant' not 'waterproof.'
The fabric is "tested against a high pressure water stream from any angle" and a minimum of 3 folds of the roll-top closure is good enough for all other drybag manufacturers, so one must assume LowePro's caution is down to a fear of liability for lots of expensive camera equipment.
The result is a pack that performs much better than claimed - the durable fabric gives huge confidence in the water, and although I never submerged the pack, I'm sure it would cope with a couple of minutes accidentally overboard.
Where it falls down, is as a backpack. The straps are necessarily stuck on, rather than integrated into the pack (where they would create weak points in the water resistancy), but they don't seem to be in the right place (the pack is very top heavy) and are a little flimsy. It may not be ideal for hikers, but the straps do make for a welcome convenience on short portage routes.
The pack is at its best sitting in a canoe giving enormous peace of mind to the novice paddler. It's a little on the large side to be kept handy in a kayak, but the smaller Dryzone DF 20l (£124) is absolutely perfect in that scenario, sliding between the legs and holding a DSLR plus extra lens, ready for rapid deployment.
In terms of value, for the bad weather hiker, a better rucksack with a drybag liner would be a much cleverer investment. For the rough and tumble of a canoe trip though, this is a great product.