Instead of a simple mesh water-bottle pocket on one or both sides of the pack, the Synapse hosts a zippered, vertical center pocket that's deep and wide enough to hold a 32-ounce water bottle; an O-ring lets you hang a hydration bladder. Besides being much more secure than a short, open-top, mesh pocket, the Synapse's central compartment keeps your bag balanced on your back, no matter how heavy the bottle. Just in front of this pocket is a smaller zippered pocket that's perfect for your phone, a wallet, your earbuds, or other small items.
On each side of the water-bottle pocket are two sizable vertical pockets, each large enough to fit a small umbrella or even a light windbreaker. Each of these pockets includes an O-ring and one or more organizational pouches: three pen/stylus holders in the left-hand pocket, and a larger, soft-lined pouch for your phone in the right-hand pocket. The company includes one removable, 8-inch key strap that attaches to any of the bag's O-rings.
Across the bottom of the bag, in the front, is the fifth zippered compartment, this one also significantly larger than its counterpart on the Synapse 19. In fact, on the Synapse 25 it's large enough for a sweater or light jacket, or even some gym clothes. This pocket also includes three O-rings — sense a pattern? — for attaching one of Tom Bihn's many organizational accessories. On the outside of this pocket is a webbing loop for attaching a safety light while walking or biking.
Everyone has their own pocket/organization preferences, but I've found the Synapse's design to offer a great balance between enough pockets to keep everything organized, but not so many that you end up obsessing over where everything goes (or trying to remember where you put it).
On the rails
Speaking of organization, the big feature addition compared to the Synapse 19 is that the Synapse 25 incorporates two sets of webbing loops for Tom Bihn's clever "checkpoint friendly Rails system." This allows the Synapse 25 to accommodate not one, but twoCache seeves. These sleeves, which are available in vertical and horizontal orientations for pretty much any size tablet and laptop (up to 15 inches), don't offer any rigid panels, but they do offer decent shock protection.
But the best part of the Cache/Rails system is that the combination makes it easy to get your laptop and/or tablet out of the backpack, and turns the Synapse 25 into a TSA-checkpoint-friendly bag. Each $30 Cache sleeve includes two full-length, nylon-webbing strap that Tom Bihn calls rails, as well as (for $5 more) a pair of Gatekeeper Rail Clips. Attach one end of each clip to a rail, and the other to one of the Synapse's webbing loops, and the sleeve is held securely in the bag. But when you get to an airport checkpoint, you just open the main compartment and slip the Cache sleeve right out of the bag — the clips slide freely along the rails until stopping at the bottom of the sleeve. The Cache remains firmly attached to the Synapse, but the sleeve is now completely exposed so that TSA agents can clearly view your laptop in the X-ray.
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