From the Revelate Designs website:
"The Gas Tank™ is more than just another top tube bag, it offers substancial storage in an easy access case. Zip open a side for one-handed access while riding, open up both for full panel access to your contents .
Fill it with M&M's, tools, a camera, bear spray, whatever. It's fully padded with closed cell foam and lined with light fabric.
Features a full wrap around water resistant zipper, hook and loop interior divider and a contoured stem mounting strap. The main top tube strap has gripper material with a double back wrap for bomber stability.