"The Traverse 40 has what Exped calls a Switchback frame, that lets you curve the frame of the backpack on demand in order to increase the amount of ventilation between the pack and your back. 

When it’s not needed, you can release the Switchback system, and the frame will return to it original flat state.

While ventilated backpack frames are comfortable, they can throw you off-balance because they move the concentrated mass of a backpack load farther away from your hips and abdominal muscles. This is most noticeable when you’re scrambling and the added momentum of the load can result in a fall. The Switchback frame system lets you choose when you want a curved and ventilated pack, vs a flat one, with very little added weight over a conventional frame."

Click here for the full review at SectionHiker.com.