 Since the slapper impacts a wide area - 40 thousandths of an inch (roughly one mm) across - of the explosive, rather than a thin line or point as in an exploding foil or bridgewire detonator, the detonation is more regular and requires less energy.Reliable detonation requires raising a minimum volume of explosive to temperatures and pressures at which detonation starts.If energy is deposited at a single point, it can radiate away in the explosive in all directions in rarefaction or expansion waves, and only a small volume is efficiently heated or compressed.