Napalm was made by dissolving a thickening agent into liquid fuel, most commonly gasoline, to produce a sticky gel that burned far longer and at higher temperatures than the fuel alone. The original World War II formula combined aluminum salts of naphthenic acid and palmitic acid with gasoline, and the weapon’s name is a portmanteau of those two ingredients. The chemistry evolved substantially over the following decades, but the core principle never changed: turn a fast-burning liquid into something that clings, spreads, and keeps burning.
The Original WWII Formula
The problem military researchers were trying to solve in the early 1940s was straightforward. Gasoline burns hot, but it splashes and evaporates quickly. A firebomb filled with plain gasoline would ignite in a flash and burn out almost as fast, limiting its effectiveness against structures and fortifications. What the military needed was a way to make gasoline behave more like a thick paste, something that would stick to surfaces and burn at a controlled rate.
A team at Harvard led by chemist Louis Fieser found the answer by creating what chemists call a metallic soap. By combining aluminum with naphthenic acid (a byproduct of petroleum refining) and palmitic acid (a fatty acid found in coconut and palm oil), his team produced a fine powder that, when stirred into gasoline, transformed the liquid into a thick, brownish gel. The aluminum atoms in these soap molecules acted as cross-linking points, creating a loose molecular network that trapped the gasoline and prevented it from flowing freely.
The mixing process was simple by design, because the military needed to produce the weapon quickly and in staggering quantities. The powdered thickener was shipped separately and combined with gasoline at or near the point of use. Soldiers or technicians poured the powder into drums of gasoline and stirred, sometimes by hand, sometimes mechanically. Within minutes the gasoline thickened into a gel that could be loaded into incendiary bombs or flamethrower tanks. The ratio of thickener to gasoline was adjustable: more powder yielded a stiffer gel that traveled farther from a flamethrower, while less powder produced a thinner mixture that spread more readily on impact.
This field-mixing approach was a deliberate feature, not a limitation. Shipping pre-mixed napalm in bulk would have been far more dangerous and logistically difficult than shipping inert powder and liquid fuel separately. The ability to mix on site also let different units tailor the consistency for their specific weapons and targets.
How the Gel Changed Everything
The transformation from liquid to gel was the entire innovation. When gasoline is ignited as a liquid, it burns at its surface and evaporates rapidly. A pool of burning gasoline on a flat surface might burn itself out in under a minute. But when that same gasoline is trapped in a gel matrix, the fuel is released gradually as the gel breaks down under heat. This extends burn times from seconds to several minutes, and in some formulations, up to ten minutes or more.
The gel also gave napalm its notorious stickiness. Because the thickened fuel resisted flowing until a certain force was applied, it adhered to whatever it landed on. Splashed onto a wall, a vehicle, or skin, it stayed in place and kept burning. This property is characteristic of gelled fuels in general; they behave as near-solids at rest and flow like thick liquids only when pushed past a threshold force. Research on modern kerosene-based gels has confirmed this shear-thinning behavior quantitatively, showing that gelled fuels have a measurable yield stress below which they act essentially as solids.1PubMed Central. Rheological Properties of Organic Kerosene Gel Fuel
The practical result was a weapon that could penetrate structures, flow into bunkers and tunnels on detonation, then re-thicken on whatever surface it settled on. The combination of adhesion and extended burn time meant that napalm could ignite materials that would normally resist brief exposure to flame. Concrete, metal, damp wood, and even partially submerged surfaces could be set ablaze because the burning gel stayed in contact long enough to transfer its heat.
Napalm-B and the Vietnam-Era Reformulation
By the mid-1960s, the original aluminum-soap formula had been replaced by a significantly different composition known as Napalm-B, sometimes called “super napalm.” This version abandoned the metallic soap approach entirely in favor of a plastic-based thickener.
Napalm-B consisted of roughly equal parts benzene and gasoline, thickened with polystyrene, the same plastic used in disposable cups and packing foam. When polystyrene dissolves in a mixture of benzene and gasoline, it forms a viscous, syrupy gel. The polystyrene molecules are long-chain polymers that physically entangle with one another in solution, creating the gel structure without metallic cross-links. The mechanism is different from the aluminum-soap version, but the end result is the same: a clinging, slow-burning gel.
The shift to polystyrene brought several advantages. The new formula was cheaper to produce, more stable in storage, and easier to ignite reliably. It also burned hotter, with estimates placing Napalm-B flame temperatures between roughly 800 and 1,200 degrees Celsius. The polystyrene itself contributed fuel to the fire, and the benzene component helped sustain an intense, oxygen-hungry flame. Where the original WWII napalm could sometimes be scraped off a surface or partially extinguished with water, Napalm-B clung more tenaciously and re-ignited readily.
Manufacturing Napalm-B at industrial scale involved dissolving commercial polystyrene pellets into tanks of mixed benzene and gasoline. Quality control focused on achieving consistent viscosity. Too little polystyrene and the mixture was too runny to stick on impact. Too much and it became too stiff to disperse properly when the bomb casing ruptured. The finished gel was loaded into bomb casings, most commonly the Mark 77 series, which used a small bursting charge to split the casing open and an igniter to light the gel as it spread.
Why Napalm Was So Lethal
The lethality of napalm went well beyond its ability to cause burns, though the burns alone were catastrophic. Because the gel adhered to skin and clothing, it was nearly impossible to remove while burning. Victims suffered deep burns that destroyed skin, underlying tissue, and sometimes bone. The extended burn time of the gel meant that even brief contact could produce full-thickness injuries that were extremely difficult to treat.
But the damage extended to anyone in the vicinity, not just those hit directly. Burning napalm rapidly consumed oxygen in the surrounding area, creating localized zones of suffocation. The combustion products included dangerously high concentrations of carbon monoxide and carbon dioxide, both of which can be lethal in enclosed or semi-enclosed spaces.2PubMed. Napalm Toxicity People sheltering underground during an aerial napalm attack could die of asphyxiation or carbon monoxide poisoning without ever being touched by flame. The delivery devices themselves added blast injury to the equation, meaning that victims near the point of impact faced an overlapping combination of explosion, thermal burns, oxygen depletion, and toxic gas inhalation.2PubMed. Napalm Toxicity
Medical treatment for napalm burns was notoriously difficult even in well-equipped hospitals. The burns tended to be deeper and more contaminated than those from other thermal sources, because the gel embedded itself in tissue and the chemical residue complicated wound care. Survival rates improved over the decades as burn medicine advanced, but the injuries remained among the most devastating a person could suffer.
The Homemade Myth
Popular culture, particularly the novel and film Fight Club, popularized the idea that napalm could be easily made at home with grocery-store ingredients. The fictional recipe involving orange juice concentrate and gasoline is chemically nonsensical. Citric acid and sugar do not polymerize gasoline, and the resulting mixture would behave nothing like actual napalm.
The real chemistry, while not requiring exotic materials, demanded industrial-grade components and careful formulation. The original WWII version needed specifically processed aluminum salts manufactured in chemical plants. Napalm-B required benzene, a known carcinogen with strict handling and storage requirements, along with bulk polystyrene and gasoline mixed under controlled conditions. These were not kitchen-counter operations.
Various improvised incendiary mixtures have existed throughout history. Thickened gasoline made with dissolved rubber, melted Styrofoam, or soap flakes can produce something that burns while clinging to surfaces. But these crude mixtures lack the carefully tuned viscosity, ignition reliability, and sustained burn characteristics of military-grade napalm. The gap between a crude thickened-fuel experiment and a deployable weapon system is vast, and attempting to bridge it is both extremely dangerous to the person trying and illegal in most countries.
International Restrictions and the End of Military Napalm
The United Nations Convention on Certain Conventional Weapons adopted Protocol III in 1980, restricting the use of incendiary weapons against civilian populations and against military targets located within concentrations of civilians. The protocol specifically covers weapons designed to set fire to objects or cause burns through flame or heat, a category that includes napalm squarely.
The United States signed the convention but did not ratify Protocol III until 2009, and even then with reservations preserving the right to use incendiary weapons when their use would result in fewer civilian casualties than alternatives. The American military officially retired its napalm bombs in 2001, replacing them with weapons using different incendiary formulations. The Mark 77 Mod 5 bomb used in the 2003 Iraq conflict contained a kerosene-based fuel gel rather than the benzene-polystyrene mixture of Napalm-B. Military officials maintained that the new weapon was categorically different from napalm, though critics noted that its effects on the ground were essentially indistinguishable.
Several other countries developed their own napalm or napalm-equivalent weapons during the Cold War. Soviet-era incendiary weapons used thickened fuel variants, and various armed forces experimented with gelled-fuel incendiaries throughout the latter half of the twentieth century. The fundamental approach was always the same: dissolve or suspend a thickening agent in liquid fuel to produce a clinging, sustained-burn weapon.
Modern Gel Fuel Research
Gelled fuels remain an active area of scientific study, though the focus has shifted largely away from weaponry and toward rocket propulsion, energy storage, and industrial applications. Modern researchers investigate how different gelling agents affect the flow behavior and combustion performance of hydrocarbon fuels, using polymers, metallic particles, and organic thickeners to tune gel properties for specific engineering purposes.
Studies on kerosene-based gels, for example, have characterized their shear-thinning behavior in precise detail, measuring how viscosity drops as the applied force increases and how gelling agent concentration affects consistency.1PubMed Central. Rheological Properties of Organic Kerosene Gel Fuel This same physical property is what made napalm effective: the gel remains stable in storage and during transport, then flows and disperses when subjected to the sudden force of an explosion or a flamethrower’s propellant. Understanding these dynamics is now relevant primarily to gel-fuel rocket engines, where the fuel needs to flow smoothly through injectors while remaining stable in tanks, rather than to incendiary weapons.
The gelling agents used in current research tend to be organic thickeners or specialty polymers chosen for performance and safety rather than lethality. But the underlying physics of fuel gelation has not changed since Fieser’s laboratory in the 1940s. Trap a volatile liquid inside a molecular or polymeric network and you control when, where, and how it burns. That principle powered one of the most controversial weapons of the twentieth century, and it continues to drive engineering applications that have nothing to do with warfare.