Napalm was so destructive because it combined extreme heat, a sticky gel that clung to anything it touched, and the ability to kill even people it never directly burned by consuming all nearby oxygen. Burning at over 5,000°F (2,760°C), it reached temperatures far beyond ordinary gasoline fires, and its unique chemistry made it nearly impossible to extinguish or escape.
A Gel Designed to Stick and Burn
The destructive power of napalm starts with its chemistry. The most widely used version, Napalm-B, consisted of 43% polystyrene, 37% gasoline, and 20% benzene by weight. The polystyrene acted as a thickening agent, turning what would otherwise be a liquid fuel into a sticky, gel-like substance. This gel clung to skin, clothing, vegetation, and structures on contact. Unlike a splash of gasoline, which runs off surfaces and burns away in seconds, napalm adhered and kept burning.
The original formula, developed in 1942 at Harvard University by chemist Louis Fieser, used an aluminum soap made from a blend of naphthenic and other fatty acids to thicken gasoline. The name “napalm” itself came from shortening “naphthenic” and “palmitic,” two of the acids in that original thickener. Fieser’s team created it because natural rubber, which had previously been used to thicken gasoline for incendiary weapons, was in short supply during World War II. The later Napalm-B formula replaced the aluminum soap with polystyrene, producing a gel that was even more stable, burned longer, and was harder to remove from skin.
Temperatures That Melt Metal
Once ignited, napalm burns at more than 5,000°F (2,760°C). For comparison, steel melts at around 2,500°F, and standard gasoline burns at roughly 1,500°F. This extraordinary heat meant napalm could destroy reinforced structures, vehicles, and weapon emplacements that conventional explosives might only damage. It could burn through sheet metal and ignite materials that would otherwise resist fire.
The polystyrene in the mixture played a critical role here. As it burned, it produced an intensely hot, slow-consuming flame rather than a quick flash. A pool of gasoline might burn out in under a minute. Napalm could burn for several minutes, and in concentrated quantities, much longer. That sustained heat was what made it so effective at destroying hardened targets and starting fires that spread well beyond the initial point of impact.
Burns That Reached the Bone
The combination of extreme temperature and prolonged skin contact produced some of the most severe burn injuries in modern warfare. Because the gel stuck to the body and could not be wiped or washed off easily, it continued burning through successive layers of tissue. Victims routinely suffered fourth-degree burns, the deepest classification, where fire destroys not just all layers of skin but penetrates into the underlying muscle, tendon, and bone.
Water was largely ineffective against napalm burns. The gel repelled water, and some formulations could even reignite after being temporarily smothered. Survivors of napalm attacks frequently required years of reconstructive surgery and lived with severe disfigurement and chronic pain. The psychological toll on survivors and witnesses was equally devastating, a reality that became central to public opposition to its use during the Vietnam War.
Killing Without Direct Contact
One of napalm’s most insidious qualities was its ability to kill people it never touched. When napalm burned in or near enclosed spaces like bunkers, tunnels, or buildings, it rapidly consumed the available oxygen. People inside these spaces lost consciousness and died from asphyxiation within minutes, even if the flames never reached them directly.
The combustion also generated dangerous levels of carbon monoxide and carbon dioxide. Carbon dioxide, being denser than air, settled into the lowest points of the terrain: foxholes, ditches, basement levels, and tunnel systems. In these low-lying areas, elevated carbon dioxide concentrations could persist for hours because cross-currents couldn’t easily disperse the heavy gas. Carbon monoxide, roughly the same density as ambient air, spread more readily but was equally lethal, poisoning anyone who inhaled it before ventilation could clear the area.
In open areas, the oxygen depletion resolved within seconds to minutes as fresh air moved in. But in the confined spaces where soldiers often sheltered during air attacks, the combination of oxygen loss and toxic gas buildup turned napalm into something closer to a chemical weapon than a conventional incendiary. This made it particularly effective against fortified positions, cave complexes, and underground networks, which were common in the Pacific theater of World War II and later in Vietnam.
Why It Was So Effective as a Weapon
Napalm’s destructiveness wasn’t just about any single property. It was the combination of factors working together. The gel spread across a wide area on impact, covering targets that a single explosive blast might miss. It stuck to whatever it hit, making escape or removal extremely difficult. It burned hot enough and long enough to destroy nearly any material. And it created a toxic, oxygen-depleted environment that extended the kill zone well beyond the visible fire.
Military planners valued napalm for its ability to clear dense vegetation, destroy supply lines, and neutralize entrenched defenders who were otherwise protected from conventional bombs and artillery. During the Vietnam War, the U.S. dropped an estimated 388,000 tons of napalm. Its use against forested areas was intended to eliminate cover, but the weapon inevitably struck villages and civilians, producing images of suffering that became defining symbols of the conflict.
International Restrictions on Incendiary Weapons
The scale of civilian harm eventually led to international action. In 1980, the United Nations adopted Protocol III of the Convention on Certain Conventional Weapons, which specifically addressed incendiary weapons like napalm. The protocol prohibits, in all circumstances, making civilians the object of attack with weapons primarily designed to cause burn injuries or set fire to objects. It also restricts the use of air-delivered incendiary weapons against military targets located within concentrations of civilians.
The protocol did not ban napalm outright. It restricted how and where it could be used, and not all major military powers ratified it with the same commitments. The United States, for instance, did not ratify Protocol III until 2009. Napalm and similar incendiary weapons remain legal for use against purely military targets in areas without civilian populations, though their actual deployment has become rare in modern conflicts.