High explosive anti-tank (HEAT) rounds are made of an explosive shaped charge that uses the Neumann effect (a development of the Munroe effect) to create a very high-velocity jet of metal in a state of superplasticity that can punch through solid armor.

The jet moves at hypersonic speeds (up to 25 times the speed of sound) in solid material and therefore erodes exclusively in the contact area of jet and armor material. Spacing is critical, as the jet disintegrates and disperses after a relatively short distance, usually well under 2 metres. The jet material is formed by a cone of metal foil lining, usually copper, though tin foil was common during the Second World War.

The key to the effectiveness of a HEAT round is the diameter of the warhead. As the penetration continues through the armor, the width of the hole decreases leading to a characteristic "fist to finger" penetration, where the size of the eventual "finger" is based on the size of the original "fist". In general, HEAT rounds can expect to penetrate armor of 150% to 250% of their width, although modern versions claim numbers as high as 700% .

HEAT rounds are less effective if they are spinning, the normal method for giving a shell accuracy. The centrifugal force disperses the jet, so the warhead design needs to be fired from smoothbore weapons, or else modified for use with rifled guns. A further problem is that if the warhead is contained inside the barrel, then its diameter is restricted to the caliber of the gun. Increasing the caliber to allow a greater diameter makes the gun heavier. Recoilless rifles using lighter barrels and mounts firing HEAT rounds (e.g. the British WOMBAT or Swedish Carl Gustav) have proven to be effective.

Where HEAT is used as the warhead for guided missiles, rifle grenades and spigot mortars, warhead size is not a limiting factor, as these are not contained within the firing weapon's barrel.

Contrary to a widespread misconception, HEAT rounds do not depend in any way on thermal phenomena for their effectiveness. In particular, the shaped charge jets do not "melt their way" through armor. This confusion is merely an unfortunate side-effect of the name HEAT.