What Is Resin?
Quick answer: Resin is a viscous liquid — natural (like pine resin) or synthetic (like epoxy, UV, polyester, or polyurethane) — that hardens into a solid, glass-like material through a chemical reaction called curing. As a resin material, it’s used across crafts and industry: jewelry, tabletops, coatings, adhesives, and structural composites.
Choosing a resin for a project? Our which-resin-for-which-project guide matches epoxy, UV and casting resin to what you’re making, with the gear list for each.
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🧰 Recommended Kit for This Project
- Let’s Resin Sphere & Pyramid All-in-One Kit — a 16 oz 1:1 epoxy set, four silicone molds, a 12-color glitter set, dried flowers, cups, stir sticks, droppers and gloves in one box
- 5 mil Nitrile Gloves — skin protection for every pour, thin enough for real dexterity
- NoCry Anti-Fog Safety Goggles — splash protection that will not fog up mid-pour
What is resin, exactly?
Resin is a material that starts as a liquid and becomes a solid. Before it cures, its molecules are small and loose, which is why it pours and takes the shape of a mold. As it cures, those molecules link into long chains and networks (it’s a polymer), and the liquid sets into something hard.
There are two families:
- Natural resins come from trees and insects. Pine resin is the sticky fluid that oozes from pine trees, and rosin is what’s left when it’s distilled. Amber is fossil tree resin. Shellac comes from the secretions of the lac insect. Dammar is a hard varnish resin from trees in Southeast Asia.
- Synthetic resins are made in a factory. These are what crafters mean by “resin”: epoxy, UV resin, polyester and polyurethane.
Liquid resin is what you buy. Epoxy comes as two bottles of liquid that react once you mix them. UV resin is one bottle that stays liquid until UV light hits it. Once cured, craft resin is rigid, glossy and water-resistant, but it isn’t heat-proof: cured craft epoxy can start to soften at about 120°F (50°C).
Cured resin is a thermoset, which means it doesn’t melt back into a liquid when heated. Is resin a plastic? Technically yes; here’s how it differs.
What are the main types of resin?
Four kinds of synthetic resin cover almost everything you’ll see in a craft store or a boatyard. Epoxy has two rows in the table because coating and casting epoxy behave very differently.
| Type | How it hardens | Typical mix | Typical layer | Best for |
|---|---|---|---|---|
| Epoxy (coating) | Resin + hardener react | 1:1 by volume is common (ArtResin, TotalBoat TableTop); some are 2:1. Per label | About 1/8 in self-levels (ArtResin); up to 1/4 in per layer (TotalBoat TableTop) | Coasters, trays, tabletops, coating art |
| Epoxy (casting / deep pour) | Same reaction, slower | 1:1 or 2:1, per label (TotalBoat ThickSet 1:1, Fathom 2:1) | 1/2 in to 3 in per layer, depending on the product and the size of the pour (TotalBoat) | Thick castings, river tables |
| UV resin | Hardens under a UV lamp (365–405 nm) | Nothing to mix | No thicker than 2 mm (about 1/16 in) per layer (Let’s Resin) | Jewelry, charms, small coatings |
| Polyester | Resin + a small dose of MEKP catalyst | Catalyst amount per label | Per label | Fiberglass, boat and car repair |
| Polyurethane | Two parts react, very fast | 1:1 by volume for Smooth-Cast 300; per label | Per label | Casting parts to paint, props |
Work out how much resin your mold needs →
Epoxy is the one most beginners start with. It’s two parts, a resin and a hardener, and the ratio has to be exact. Measure the way your label says: a ratio “by volume” isn’t the same as “by weight”. TotalBoat TableTop, for example, is 1:1 by volume but 1.2:1 by weight. Coating epoxy is thin and made for flat surfaces. Casting epoxy cures slowly so thick pours don’t overheat. Casting vs coating resin explains when to use which, and how to mix epoxy resin covers the measuring.
UV resin is a single liquid that hardens in minutes under a UV lamp, so there’s nothing to measure. The catch is depth: UV light only reaches so far, so you build it up in thin layers. UV resins are typically acrylic (acrylate) resins, not epoxy, even when a listing calls them “epoxy UV”. In a 2026 report in the journal Contact Dermatitis, three hobbyists developed skin allergies from resins sold that way, and testing found acrylates in them. Wear gloves even though there’s nothing to mix. UV resin for beginners · Epoxy vs UV resin
Polyester is the workhorse of fiberglass: boats, car panels, tubs and showers. Instead of a measured hardener, you harden it with a small dose of MEKP catalyst, measured the way the label says. I laminated with it at a boat builder before I moved to epoxy for crafts. Most polyester resin gives off styrene vapor, which can cause headaches, dizziness and eye irritation. The MEKP catalyst “can severely irritate and burn the skin and eyes”, according to the New Jersey Department of Health. Skip it unless you’re repairing fiberglass and can work outdoors or with real ventilation.
Polyurethane casting resin is fast. Smooth-Cast 300 gives you 3 minutes of working time and demolds in about 10. It’s also moisture sensitive: Smooth-On says “all liquid urethanes are moisture sensitive”, so keep the lids on and your cups dry. I worked with it at the boat builder too. Polyurethane systems contain isocyanates, which NIOSH says can cause or worsen asthma, whether you breathe them or get them on your skin. Skip it unless you’re casting parts to paint and have proper ventilation.
How does resin harden?
Curing is a chemical reaction, not drying. In epoxy, the resin and hardener molecules bond into a network, and the reaction gives off heat as it goes. That’s why the ratio matters so much: with too much or too little hardener, some of the resin never reacts and stays soft or sticky.
Two things slow a cure more than anything else: cold and humidity. Aim for a room at 70–80°F (21–27°C) with humidity at 60% or lower, and check your label, because makers differ. My own first two pours with the same kit show the difference. In a cool garage the resin was still rubbery at 26 hours, past the 8–24 hours the label gives for demolding. With the work area warmed to about 85°F, it set within a day and was scratch-hard at two days (the full kit review).
Need warmth? Use a heat lamp or a curing box at 85°F (29°C) or below, never a kitchen oven. A UV lamp won’t help: it cures UV resin, not epoxy.
Most craft epoxy is usable after about 72 hours and reaches full hardness at about 7 days. How long resin takes to cure has the detail. If yours stays tacky, start with why is my resin sticky? or the common resin problems guide.
What is resin used for?
- Crafts: jewelry, coasters, trays, keychains and poured art.
- Woodworking: river tables, bar tops, and filling knots and cracks.
- Coatings and floors: epoxy floor and countertop coatings.
- Electronics: “potting”, where a component is fully sealed in resin.
- Boats and cars: polyester and epoxy fiberglass for hulls, body panels and repairs.
- Dentistry: tooth-colored fillings are resin-based, and dentists harden them in the mouth with a curing light.
A short history of resin
Natural resins came first. Amber is fossil tree resin, and shellac, from the lac insect, is still a traditional wood finish. The first synthetic resin was Bakelite, invented in 1907 by Leo Baekeland; its patent is often counted as the start of the modern plastics industry. Epoxy came later: the chemist Pierre Castan developed an epoxy resin in 1936, and the company Ciba brought it to market as Araldite in 1946.
Ready to try it?
Start small. How to start resin crafting covers what to buy first, the essential tools list covers the gear, how to mix epoxy resin walks through measuring and mixing, and the coaster tutorial is a good first project.
Before you open the bottles
- Uncured epoxy can cause a skin allergy (sensitization), and the more often your skin is exposed, the more likely it is. Uncured UV resin can too. Wear nitrile gloves every time, plus safety glasses or goggles.
- Work with real airflow, like an open window and a fan pulling air out. If you can’t, wear a respirator with organic-vapor cartridges.
- Wear an N95 mask when sanding, and never sand resin that isn’t fully cured.
- Resin in your eyes: flush with water for 15 minutes. If it still hurts, get medical help. On your skin: wipe it off, use a waterless hand cleaner, then soap and warm water. Never use solvents on skin.
- More: Resin Safety Hub · Resin PPE for beginners
Leftovers: a cup of mixed epoxy heats up as it cures, and a big mass can get hot enough to melt plastic or start a fire. Spread leftovers in a wide, shallow tray away from anything that can burn, rather than leaving them in the cup. For liquid resin you won’t use, check your local hazardous-waste rules. Is resin plastic? covers recycling and disposal.
Frequently Asked Questions
What is a resin?
Resin is a viscous liquid — natural (like pine resin) or synthetic (like epoxy, UV, polyester, or polyurethane resin) — that hardens into a solid, glass-like material through a chemical reaction called curing.
What is resin material?
Resin material is the liquid you pour or brush on before it hardens. Most craft resin is epoxy, sold as two parts (a resin and a hardener) that react when mixed. UV resin is a single liquid that hardens under a UV lamp. Polyester and polyurethane are the other common resin materials, used mostly for fiberglass and fast casting.
What is resin used for?
Resin is used for jewelry, coasters, tabletops and poured art in crafts, plus fiberglass boats and car parts, floor coatings, sealing electronics, and dental fillings.
What is resin made of?
Epoxy is two components: the uncured resin and a curing agent, or hardener, which is usually an amine. UV resin is a mix of monomers and oligomers (small and medium building-block molecules) plus a photoinitiator that starts the reaction when UV light hits it. Craft UV resins are usually acrylates. For petroleum-based versus “bio-based” resin, see is resin plastic?
Is epoxy the same as resin?
No. Epoxy is one type of resin, and the most common one in crafts. “Resin” also covers UV resin, polyester and polyurethane, which cure differently and need different precautions. Watch for labels like “epoxy UV resin”: UV resins are usually acrylates, not epoxy.
Sources
- ArtResin FAQ: self-levels to about 1/8 in (3 mm); measure by volume, not weight; heat resistance up to 120°F (50°C)
- TotalBoat TableTop Epoxy: up to 1/4 in per layer; 1:1 by volume, 1.2:1 by weight
- TotalBoat ThickSet and Fathom deep pour epoxy: pour depth per layer and mix ratios
- Let’s Resin, Know More About UV Resin: UV light between 365 and 405 nm
- Let’s Resin Pearlescent UV Resin: single layer no thicker than 2 mm
- Raison-Peyron et al., Contact Dermatitis (2026): hobby “epoxy UV” resins contained (meth)acrylates and caused skin allergies
- DermNet, Allergy to acrylates: acrylates as a contact allergen
- Smooth-On Smooth-Cast 300: 1:1 by volume, 3-minute pot life, 10-minute cure, moisture sensitive
- OSHA, Styrene: health effects of styrene exposure
- NIOSH, Styrene exposure in fiberglass boat manufacturing: styrene in fiberglass work
- New Jersey Department of Health, MEKP fact sheet: skin and eye burns
- NIOSH, Isocyanates: asthma risk from breathing or skin contact
- WEST SYSTEM, Health Effects from Overexposure to Epoxy: sensitization; sanding partly cured epoxy
- WEST SYSTEM, Preventing Overexposure: ventilation, organic-vapor respirator, N95 for dust, eye flushing
- WEST SYSTEM, Uncontrolled Cure: heat from mixed epoxy; use a wide, shallow container
- NIOSH Health Hazard Evaluation 2007-0355-3102: what epoxy systems are made of
- RadTech, The UV & EB Curing Process: monomers, oligomers and photoinitiators
- American Dental Association, Dental Curing Lights: light-cured resin restorations
- Britannica, Bakelite: invented in 1907; the first synthetic resin
- Britannica, amber: fossil tree resin
- Britannica, shellac: made from the lac insect
- Britannica, rosin: distilled from pine oleoresin
- Britannica, dammar: hard varnish resins from Asian trees
- Historical Dictionary of Switzerland, Pierre Castan: epoxy 1936; Araldite 1946
Keep Learning on ResinAffairs.com
Now that you know what resin is and how it cures, here’s where to go next:
- ♻️ Is Resin Plastic? → — how resin compares to everyday plastics, and what that means for the environment.
- ⚖️ Epoxy Resin vs. UV Resin → — which resin type suits your first project, compared side by side.
- 🚀 How to Start Resin Crafting → — the beginner roadmap: what to buy first, what to skip, and the easiest first project.
- 🫧 Visit the Resin Safety Hub → — what to know about handling resin safely before you start.
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