Firecrackers are generally made of cardboard or plastic, with flash powder or black powder as the propellant. This is not always the case, however. Anything from match heads to lighter fluid have been used successfully in making firecrackers. The key to loud firecrackers, however, although in part lying in the propellant substance, is pressure. The entire firecracker must be very tightly packed in order for it to work best. Flash powder, however, does not need to be packed tightly, and should not be.