Timbuk2 Clear Flex Accessory Pack, Gunmetal/Blue/Gunmetal, X-Small Durable ballistic nylon and clear urethane exterior Fog-proof clear window gives you and a no-nonsense view of your precious potions. XS and S will glide through checkpoints, but the M is too big to make the carry-on cut. Fully lined to prevent cross-contamination. Zipper closure for easy in and out.