Most resin used in crafting, coating, and manufacturing is not eco-friendly. Standard epoxy and polyester resins are derived from petroleum, release volatile organic compounds as they cure, cannot be meaningfully recycled once hardened, and persist in the environment indefinitely. Bio-based alternatives exist, but even the greenest commercial options still contain 40% to 70% synthetic ingredients.
What Standard Resin Is Made Of
Over 85% of epoxy resins on the market are made by reacting two petroleum-derived chemicals: epichlorohydrin and bisphenol A (BPA). These are combined with hardeners and sometimes diluents or styrene to adjust the resin’s viscosity and curing speed. Polyester resins, commonly used in fiberglass and casting, similarly rely on fossil fuel feedstocks and often contain styrene as a reactive solvent.
Once these components are mixed and cured, they form a thermoset plastic. Unlike a water bottle or food container, thermoset plastics have a permanently crosslinked molecular structure. They cannot be melted down and reshaped, which is the fundamental reason they’re so difficult to deal with at end of life.
Air Quality During Curing
Resin releases volatile organic compounds throughout its curing process, and the amounts can be surprisingly high. Research on resin curing found emissions including formaldehyde, benzene, xylenes, styrene, acetaldehyde, and various methacrylate monomers. Post-processing steps like UV curing or heat curing can produce a twenty-fold spike in VOC emissions compared to the initial mixing and pouring phase, though completing the full cure cycle ultimately reduces ongoing emissions by about tenfold compared to leaving resin partially cured.
For hobbyists working in a garage or studio, this means proper ventilation matters not just during pouring but especially during curing. The chemicals released are not just unpleasant to breathe. Formaldehyde and benzene are recognized carcinogens, and styrene is classified as a possible carcinogen. These compounds contribute to indoor air pollution and, when released outdoors, participate in smog formation.
What Happens After Resin Hardens
Fully cured epoxy resin is chemically stable. Lab testing on cured epoxy samples has shown no detectable leaching of toxic agents into surrounding environments, and cell viability tests (a standard measure of toxicity) showed no cytotoxic effects. So a finished resin coaster or piece of jewelry sitting on your shelf is not actively poisoning anything around it.
The environmental problem is what happens when resin objects are damaged, sanded, or discarded. Grinding or finishing cured resin produces microparticles ranging from nanoscale to about 10 micrometers, small enough to become airborne or wash into waterways. These particles are, functionally, microplastics. They don’t biodegrade. In dental applications alone, where resin composites are routinely ground and polished, an estimated 12 tonnes of resin microparticle waste enters municipal wastewater annually in the UK. Scale that concept to every workshop, factory, and hobbyist sanding resin, and the cumulative load is significant.
Recycling Is Barely an Option
Cured thermoset resin cannot be melted and reformed the way thermoplastics like polyethylene can. This is the core recycling challenge: the same chemical crosslinking that makes resin hard and durable also makes it nearly impossible to reprocess.
Three recycling approaches exist in theory. Mechanical recycling grinds cured resin into fine particles that can be used as filler material, but the recovered material has poor mechanical properties and limited usefulness. Chemical recycling uses solvents and catalysts to break down the crosslinked structure, but it remains difficult to scale beyond the laboratory. Thermal recycling (pyrolysis) heats resin to extreme temperatures, around 600°C, to recover some energy or chemical feedstock, but it produces CO2 emissions and can generate toxic byproducts like bromine compounds that need to be removed first. Only a handful of industrial plants worldwide currently operate pyrolysis for thermoset waste.
For home users, the practical reality is that cured resin goes in the trash. Uncured liquid resin is more concerning. Under U.S. federal regulations, waste is classified as hazardous if it’s ignitable, corrosive, reactive, or toxic. Liquid resin can meet several of those criteria. However, household waste is categorically excluded from hazardous waste regulations, meaning home crafters can legally dispose of small amounts in regular garbage. The responsible approach is to fully cure any leftover resin before disposal, since hardened resin is chemically inert while liquid resin can leach into soil and groundwater.
Bio-Based Resins: How Green Are They?
A growing number of companies sell resins marketed as eco-friendly or bio-based. These products replace some petroleum-derived ingredients with plant oils, cashew nut shell liquid, or other renewable feedstocks. The key question is how much of the resin actually comes from biological sources.
Commercial bio-based epoxies typically contain between 29% and 56% bio-derived content. Some examples from a 2023 review of available products: Sicomin’s Surf Clear EVO contains about 40% vegetable oil-derived content. Entropy’s SuperSap 100 uses waste pine and vegetable oils for 37% of its composition. EcoPoxy’s BioPoxy 36 incorporates soybean oil, cashew nut oil, and recycled eggshells for 32% bio-content. Even the most bio-heavy options still rely on synthetic petrochemical components for the majority or a large minority of their formulation.
Bio-based resins are a genuine improvement over fully petroleum-derived products, but they still cure into thermoset plastics with the same end-of-life problems. They cannot be recycled any more easily than conventional resin. They still release VOCs during curing. And “bio-based” does not mean “biodegradable.” Once cured, a bio-epoxy river table will persist in a landfill just as long as one made with standard epoxy.
Natural Resins as an Alternative
True natural resins, the kind harvested from trees and insects, have a fundamentally different environmental profile. Shellac, for instance, is secreted by lac insects and is fully biodegradable and non-toxic. It takes roughly 100,000 lac bugs to produce one kilogram of shellac, but the insects are not killed in harvesting and the process supports forest ecosystems in India and Southeast Asia where lac cultivation takes place. Damar resin, tapped from tropical trees, and pine rosin are similarly renewable and biodegradable.
The tradeoff is performance. Natural resins cannot match the clarity, hardness, heat resistance, or waterproofing of synthetic epoxy. Shellac dissolves in alcohol, softens in heat, and scratches easily. These resins work well for wood finishing, food-safe coatings, and artistic applications, but they’re not substitutes for the thick, glass-clear pours that most resin crafters are after.
Reducing Your Environmental Impact
If you use resin regularly, a few practices make a measurable difference. Mix only what you need. Leftover liquid resin is the most environmentally harmful form of resin waste, and pouring excess down a drain introduces persistent chemicals into waterways. Cure all leftover resin fully before throwing it away.
When sanding or finishing cured resin, work wet whenever possible and collect the dust. Dry sanding sends microplastic particles into the air and surrounding environment. A vacuum with a fine particulate filter helps, but wet sanding captures the smallest particles in water that can then be filtered rather than released.
Ventilation during curing isn’t just a health precaution for you. It’s also an environmental consideration. VOCs released indoors eventually make it outdoors. Working in a well-ventilated space with air filtration reduces the total chemical load you’re putting into the atmosphere. Completing the full recommended cure cycle, including UV or heat post-curing if specified, reduces long-term VOC off-gassing by up to tenfold compared to resin that’s left partially cured.
Choosing a bio-based resin with higher bio-content (40% or above) reduces petroleum dependence per project. It won’t solve the disposal problem, but it does lower the upstream carbon footprint of production.