Resin comes from two very different sources depending on the type. Natural resin is produced by living trees as a sticky, protective substance made primarily of carbon-based compounds called terpenes. Synthetic resin is manufactured from petroleum-derived chemicals in industrial facilities. Both types are called “resin,” but their origins and compositions have almost nothing in common.
What Natural Tree Resin Is Made Of
Natural resin is a thick, sticky substance that trees secrete from specialized glands in their bark and wood. Its primary building blocks are terpenes, which are hydrocarbons built from repeating units of a small molecule called isoprene. These terpenes come in different sizes. Smaller ones (monoterpenes and sesquiterpenes) give resin its strong smell and initial liquid consistency, while larger ones (diterpenes and triterpenes) provide the thick, gummy texture that eventually hardens on contact with air.
Beyond terpenes, natural resin contains resin acids, esters, and alcohols. Some resins also include phenolic compounds that have antimicrobial properties. The exact chemical recipe varies by species. Pine resin, for example, is heavy in a resin acid called abietic acid, while resins from tropical hardwoods tend to be richer in triterpenes. This chemical variation is why different resins have distinct colors, smells, and hardness levels.
One important distinction: resin is not the same as sap. Tree sap is mostly water with dissolved sugars (think maple syrup). Resin is hydrocarbon-based, water-insoluble, and far stickier. They serve completely different functions in the tree, and they flow through different channels.
Which Trees Produce Resin
Conifers are the most prolific resin producers. Pines, firs, spruces, cedars, redwoods, larches, and junipers all generate significant amounts. If you’ve ever touched a freshly cut pine board and felt that tacky residue on your fingers, that’s resin.
But conifers aren’t the only source. Several flowering plant families also produce resin. Tropical tree families like Dipterocarpaceae (the dominant hardwoods of Southeast Asian forests), Burseraceae (the family that gives us frankincense and myrrh), and Anacardiaceae all secrete resin in substantial quantities. In North America, sweetgum, aspen, creosote bush, and even common herbs like dill and fennel produce smaller amounts of resinous compounds.
Why Trees Make Resin
Trees produce resin primarily as a defense mechanism. When bark is damaged by an insect boring into the wood, a bird pecking, or a branch snapping off, resin flows to the wound site and seals it. This serves a dual purpose: the sticky mass physically traps insects, and the antimicrobial compounds in the resin prevent bacteria and fungi from infecting the exposed tissue. Some trees also have glandular hairs on their leaves and stems that secrete sticky resin to deter larger herbivores from grazing.
Resin production increases dramatically when a tree is under stress. Forests that experienced high insect pressure or warm, volatile climates historically produced enormous quantities. During a roughly 54-million-year stretch of the Cretaceous period, coniferous forests produced so much resin that scientists have given it a formal name: the Cretaceous Resinous Interval. Much of the world’s amber dates to this era.
How Resin Becomes Amber
Amber is fossilized tree resin, and the transformation takes millions of years. When resin drops from a tree and gets buried in sediment, the volatile terpenes slowly evaporate and the remaining compounds undergo polymerization, linking into long, stable molecular chains. Over tens of millions of years, heat and pressure from overlying sediment complete the hardening process.
Not all buried resin becomes amber. The resin needs to be chemically stable enough to resist complete decay, and it needs the right burial conditions: low oxygen, moderate temperature, and proximity to transitional environments like river deltas or coastal wetlands where sediment accumulates quickly. Amber preserves biological material in extraordinary detail, which is why ancient insects trapped in resin can still be studied millions of years later with features intact down to individual wing veins.
What Synthetic Resin Is Made Of
Synthetic resins start as petroleum. Crude oil is refined and cracked (broken into smaller molecules using heat) to produce a feedstock called pyrolysis gasoline. This feedstock is a complex chemical soup: roughly 55% aromatic compounds, 22% olefins, and the rest a mix of other hydrocarbons. The three most abundant single chemicals in a typical feedstock are benzene (about 28%), toluene (18%), and ethylbenzene (7%).
From this starting material, manufacturers use catalysts to trigger polymerization, linking small molecules into long chains that form a solid or semi-solid resin. The specific type of resin depends on which molecules are polymerized and how. Aliphatic resins use smaller, simpler hydrocarbon chains (called C5 compounds), aromatic resins use the ring-shaped molecules (C9 compounds), and hybrid resins combine both.
Common Types of Synthetic Resin
Epoxy resin is one of the most widely used. It’s made by reacting two main chemicals: one derived from a compound found in many plastics (bisphenol A) and another called epichlorohydrin, a chlorine-containing molecule derived from petroleum. When these are combined with a hardener, they cross-link into an extremely strong, rigid material used in adhesives, coatings, and composite manufacturing.
Polyurethane resin is made by combining two classes of chemicals: polyols (compounds with multiple alcohol groups) and diisocyanates. The polyols can come from petroleum or, increasingly, from plant-based sources like liquefied palm oil biomass. When these two components react, they form a versatile polymer that can range from rigid foam insulation to flexible shoe soles, depending on the formulation.
Polyester resin, polyethylene, polypropylene, and PVC are other major categories, each with its own recipe of petroleum-derived precursors. The synthetic resin industry as a whole was valued at over $521 billion in 2024, with production measured in the hundreds of millions of tons annually.
How Natural and Synthetic Resins Compare
- Source: Natural resin comes from living trees. Synthetic resin comes from petroleum refining.
- Chemistry: Natural resin is a mixture of terpenes, resin acids, and esters. Synthetic resin is a polymerized chain of petroleum-derived monomers.
- Biodegradability: Natural resin breaks down over months to years in the environment. Synthetic resins persist for decades to centuries. PET-based resins can take over 450 years to fully degrade, and high-density polyethylene may last over 600 years.
- Environmental impact: As synthetic resins slowly fragment, they generate microplastics, particles smaller than 5 millimeters that accumulate in soil and water. These particles attract and concentrate toxic pollutants, creating a persistent environmental and health concern.
Everyday Products That Contain Resin
Natural resins show up in varnishes, incense, traditional medicines, and as the rosin used on violin bows and baseball pitchers’ hands. Pine resin derivatives called rosin esters are common in chewing gum and adhesives. Frankincense and myrrh are natural resins from Burseraceae trees that have been traded for thousands of years.
Synthetic resins are in nearly everything made of plastic, from food packaging and car bumpers to smartphone cases and house paint. Epoxy resins coat the inside of aluminum cans. Polyurethane resins form the foam in your couch cushions. Polyester resins reinforce fiberglass boats and shower stalls. If an object is plastic, composite, or coated, there’s a good chance a synthetic resin is involved.