Glue is made from different ingredients depending on the type. The white school glue in your desk drawer is a water-based emulsion of a synthetic polymer called polyvinyl acetate. The super glue in your junk drawer is an entirely different chemical: cyanoacrylate. And the oldest glues in human history were made by boiling animal bones and hides to extract collagen protein. Each type of glue bonds surfaces together through a different chemical mechanism, which is why no single glue works perfectly on everything.
White Glue and School Glue
The familiar white craft glue (like Elmer’s) is built around polyvinyl acetate, often abbreviated PVA. Manufacturers create PVA by combining a liquid chemical called vinyl acetate with a small amount of a starter compound that triggers the molecules to link into long chains. This reaction happens in water with surfactants mixed in, producing a milky white emulsion. The result is a suspension of tiny polymer particles floating in water, which is why white glue is wet when you apply it and dries clear as the water evaporates.
Most commercial PVA glues aren’t pure polyvinyl acetate. Manufacturers blend in small amounts of other compounds to make the dried glue more flexible or harder, depending on the application. School-grade versions are certified non-toxic by the Art and Creative Materials Institute and conform to ASTM safety standards, meaning they’re safe for children to handle. PVA glue bonds well to porous materials like wood, paper, and fabric, but struggles with smooth, non-porous surfaces like metal or glass because it needs to soak slightly into the material to grip.
Super Glue
Super glue is made from cyanoacrylate monomers, most commonly ethyl cyanoacrylate or methyl cyanoacrylate. These are small, reactive molecules produced by combining formaldehyde with a compound called cyanoacetic ester, then breaking the resulting polymer back down into individual molecules through high heat. The monomers are packaged in a tube with trace amounts of stabilizers like hydroquinone to prevent them from hardening inside the container. These stabilizers only work in the presence of oxygen, which is why super glue cures so quickly once squeezed out into a thin layer.
What makes super glue unique is its curing trigger: moisture. The tiny amount of water vapor on nearly any surface is enough to kickstart polymerization, causing the liquid monomers to snap together into rigid plastic chains within seconds. This is also why super glue bonds skin so effectively (and annoyingly). The same chemistry has medical applications. Surgical wound adhesives use a longer-chain version called 2-octyl cyanoacrylate, which breaks down more slowly in the body and avoids the inflammatory reactions caused by shorter-chain formulas.
Hot Glue Sticks
The solid sticks you feed into a glue gun are typically based on ethylene vinyl acetate copolymer (EVA), a rubbery plastic that melts at relatively low temperatures. EVA alone would be too soft and weak, so manufacturers blend in tackifying resins (often aromatic hydrocarbon resins) that increase stickiness, along with plasticizers that control flexibility and stabilizers that prevent the glue from degrading under heat. Some specialty formulations use nylon, polyester, or polypropylene as the base polymer instead of EVA, tailored for bonding specific materials or withstanding higher temperatures.
Hot glue works purely through cooling. There’s no chemical reaction happening. The melted polymer wets the surface, flows into tiny pores and irregularities, then solidifies as it drops back to room temperature. This makes it fast and versatile but also means the bond can soften again if exposed to enough heat.
Epoxy
Epoxy adhesives come in two parts that you mix right before use: a resin and a hardener. The resin side is typically built around a compound derived from bisphenol A, a molecule with reactive groups on both ends that can link into chains. The hardener side contains a curing agent, usually an amine compound, though anhydrides, carboxylic acids, and mercaptans are also used depending on the product. When you combine the two parts, the hardener molecules bridge between resin molecules, building a dense, cross-linked network that becomes extremely rigid and strong.
This two-part chemistry is what gives epoxy its exceptional strength and chemical resistance. Once fully cured, the bond is essentially a solid block of thermoset plastic that won’t soften with heat the way hot glue does. The tradeoff is working time: once mixed, you typically have minutes to position your materials before the reaction progresses too far.
Polyurethane Glue
Polyurethane adhesives (like Gorilla Glue) contain reactive compounds called isocyanates, commonly polymeric diphenylmethane diisocyanate (pMDI). Unlike epoxy, polyurethane glue doesn’t come in two separate bottles. Instead, it cures by reacting with moisture, either from the materials you’re bonding or from humidity in the air. When the isocyanate groups contact water molecules, they react to form new chemical bonds while releasing carbon dioxide gas. That released CO2 is why polyurethane glue foams and expands as it cures.
This foaming expansion lets polyurethane glue fill gaps and bond uneven surfaces, but it also means you need to clamp your work to prevent the pieces from being pushed apart. The cured result is a tough, waterproof bond that works on wood, metal, ceramic, and many plastics.
Animal Glue
The oldest adhesive technology on record, animal glue is made from collagen, the structural protein found in bones, hides, and connective tissues of vertebrates. The earliest archaeological evidence of collagen-based adhesive dates to roughly 8200 to 7300 BC, found coating baskets in a cave in Israel. By the fourth millennium BC, European farmers were performing basic chemical extractions to produce hide glue from cattle skins.
Collagen in its natural state is a tightly wound triple-helix protein that won’t dissolve in water. To make glue, manufacturers treat bones or hides with acids or alkalis in hot water, which unravels the protein into soluble gelatin. Different source materials produce different grades: hide glue from tannery scraps, bone glue from skeletal material, and fish glue from skins, cartilage, and swim bladders. Animal glue is still used today in fine woodworking, bookbinding, and art restoration because it’s reversible. Applying heat and moisture can soften the bond, allowing repairs without damaging the original material.
Plant-Based and Starch Glues
Starch-based adhesives are made from corn, wheat, or potato starch, all of which are complex chains of sugar molecules. In their raw form, starch granules don’t dissolve in cold water. Heating them in water causes the granules to swell and burst, releasing sticky chains that form a gel. This basic cooked starch paste is what holds corrugated cardboard together: starch mixed with water, caustic soda, and borax gets pumped onto the fluted paper layer during manufacturing.
Dextrins are a modified form of starch with shorter molecular chains, produced by heating dry starch or treating it with acid. The shorter chains dissolve more easily and dry faster, making dextrin glue ideal for envelope flaps, postage stamps, and paper labels. Chemical treatments can further tailor starch adhesives: alkali lowers the temperature at which the starch gels, acid treatment reduces thickness while keeping the glue concentrated, and oxidation with hypochlorite improves tack. These plant-based glues are inexpensive and nontoxic but only work well on paper and other porous, lightweight materials.
VOCs and Safety Considerations
Many adhesives release volatile organic compounds as they cure or dry. These are gases that evaporate from the liquid components and can irritate eyes, skin, and lungs in poorly ventilated spaces. Air quality regulations cap how much VOC an adhesive can contain: general-purpose adhesives sold in regulated districts are limited to 250 grams of VOC per liter of product. Water-based glues like PVA emit very little, while solvent-based contact cements and some industrial adhesives emit significantly more.
Cyanoacrylate (super glue) fumes can irritate the eyes and respiratory tract even in small amounts. Polyurethane glues contain isocyanates, which are a known sensitizer and can trigger allergic reactions with repeated exposure. Epoxy hardeners, particularly amine-based ones, can cause skin sensitization over time. For casual home use, the risk from any of these is low with basic ventilation. For frequent or professional use, the chemical differences between glue types matter more, and choosing a lower-emission formula becomes worth the effort.