Impromptu Science

The SodaStream canister was almost empty, time to head back to the store to trade it in for a full canister.  Lukas realized it was not completely empty and that prompted a spontaneous science experiment. Would balloons filled with carbon dioxide float, sink or remain suspended in air - ie is carbon dioxide heavier, lighter or equal to air?
The balloon fell quickly but that did not stop the boys from repeating the experiment until the canister was completely and absolutely empty.