Bulk products generally comprise a liquid phase (but also powder or paste) and are mixed inside the canister with a propellant gas that may be a liquid under pressure, such as LPG, or compressed (such as air, nitrogen, carbon dioxide). The valve and the spray button, together with propellant, emit the contents in the form of a spray, foam or powder, etc.

In the Bag-On-Valve (BOV) system, one bag is sealed directly to the valve. This consequently creates two separate compartments: the inside of the bag, which is filled with the bulk product, and an outside chamber between bag and the canister containing the propellant which, in this case, simply applies pressure on the bag during use. The BOV system offers many advantages over the traditional system, first and foremost the possibility of packaging very dense products (gel type), which are particularly sensitive to contact with gas or air, or those intended for use with foods or pharmaceuticals.