Air means it"s ultralight, made with 30D hybrid sil-nylon CORDURA. Vent means it purges air through the eVent bottom. Dry means it"s factory seam sealed with a roll-top closure, the rolling stay is pre-curved so that it pops open, making it easier to load than a flat stay. Bloc means it nests inside your pack well. Solid means it"s durable, and also that you can compress your gear down to a nearly rocksolid state. But the name doesn"t quite say it all, Lightened by replacing the compression webbing with paracord. We call it LineLoc Technology, another Granite Gear first. The Block shape is an innovation to help you pack more efficiently inside your pack. Compared to a round shape, the bloc fits better into the corners of your pack, they stack nicely, and eliminate all the "dead air" that can happen when you try to pack with round stuffsacks. Less dead air means better load stability, quicker pack loading, and the possibility of carrying the same amount of gear in a smaller pack, saving you weight.