Urethane and polyurethane are chemically different substances that share a name mostly due to industry shorthand. Urethane is a single, small molecule (ethyl carbamate) with a molecular weight of about 89 grams per mole. Polyurethane is a large polymer, a long chain of repeating units, engineered for coatings, foams, and industrial parts. When you see “urethane” on a can of floor finish, it almost always means polyurethane.
Why the Names Get Confused
The confusion is rooted in how the coatings and finishes industry talks about its products. “Urethane coating” and “urethane varnish” are common labels on store shelves, but the product inside is a polyurethane. In this context, “urethane” is just shorthand that highlights the end use rather than the full chemistry. If you’re comparing two cans at the hardware store and one says “urethane” while the other says “polyurethane,” you’re almost certainly looking at the same class of product.
The actual chemical called urethane, ethyl carbamate, is not an ingredient in polyurethane and is not released when polyurethane breaks down. The National Toxicology Program states this directly: high-molecular-weight polyurethanes used as foams, elastomers, and coatings “are not made from the chemical urethane and do not generate it upon decomposition.”
What Urethane Actually Is
True urethane, ethyl carbamate, has the chemical formula C₃H₇NO₂. It’s a small, water-soluble compound that occurs naturally in fermented foods and alcoholic beverages. It also has a history in medicine: in the 1940s and 1950s, doctors used it to treat leukemia, multiple myeloma, and other cancers, and veterinarians still use it as an anesthetic in lab animals. Outside of medicine, it serves as a solubilizer in the manufacture of pesticides, fumigants, and cosmetics, and as an intermediate in pharmaceutical production.
Ethyl carbamate carries real health concerns. The International Agency for Research on Cancer classifies it as Group 2A, meaning it is “probably carcinogenic to humans.” In animal studies, it causes dose-dependent increases in liver, lung, and other organ tumors. Limited human evidence has also linked it to a specific form of liver disease called hepatic angiosarcoma. Because it forms naturally during fermentation, the FDA has worked with the U.S. wine and spirits industries to set voluntary limits. Whiskey distillers participating in a voluntary program have brought ethyl carbamate levels down to a target of 125 parts per billion or less.
What Polyurethane Actually Is
Polyurethane is a polymer created by reacting two main components: polyols (compounds with multiple alcohol groups) and diisocyanates (reactive molecules that link the chains together). A catalyst speeds the reaction, and once all the reactive groups are consumed, you’re left with stable urethane bonds repeated thousands of times along the polymer chain. That repeating structure is what gives polyurethane its versatility.
By varying the ratio and type of starting materials, manufacturers can make polyurethanes that range from soft and rubbery to rock-hard. Hardness is measured on the Shore scale. Soft polyurethanes fall between 10 and 60 Shore A, suitable for cushioning, gaskets, and flexible seals. Medium grades sit between 60 and 90 Shore A, covering rollers, bumpers, and semi-rigid parts. Hard polyurethanes start at 60 Shore D and resist deformation under heavy loads, making them useful for wheels, structural components, and wear surfaces.
How Polyurethane Performs as a Coating
For most readers, the practical question is whether polyurethane holds up. It does, and the numbers explain why it’s so widely used. Polyurethane coatings offer strong abrasion resistance, good adhesion to a variety of surfaces, and chemical resistance. In textile testing, polyurethane impregnation increased puncture strength by 27.5% and roughly doubled water resistance compared to untreated fabric.
UV exposure is polyurethane’s main weakness. After UV weathering in lab conditions, polyurethane-treated fabric lost nearly half its puncture resistance. Adding UV stabilizers cut that loss significantly, from 48.5% down to around 22-28% depending on the stabilizer combination. For outdoor applications like deck finishes or exterior wood coatings, look for polyurethane products that include UV absorbers or plan to recoat periodically.
Quick Comparison
- Chemical identity: Urethane is a single small molecule (ethyl carbamate). Polyurethane is a large polymer chain with repeating urethane linkages.
- Health profile: Ethyl carbamate is a probable human carcinogen. Cured polyurethane is chemically stable and not made from ethyl carbamate.
- Where you’ll find urethane: Fermented foods and beverages (as a trace contaminant), veterinary anesthesia, pesticide manufacturing, biochemical research.
- Where you’ll find polyurethane: Floor finishes, foam insulation, furniture cushions, industrial rollers, automotive parts, textile coatings.
- On a product label: “Urethane finish” and “polyurethane finish” refer to the same type of coating. The word “urethane” in this context is informal shorthand for polyurethane.
If you’re shopping for a wood finish or a protective coating, the bottom line is simple: both terms on the label point to polyurethane. True urethane, the chemical ethyl carbamate, is not something you’ll encounter in a hardware store. It belongs to an entirely different world of chemistry, one involving food safety regulations and laboratory research rather than Saturday afternoon floor refinishing.