Resin vs epoxy: which type to buy
Four products share the word, and the one thing that separates them is how deep you can pour them. Pick by that, and everything else follows.
All epoxy is resin, but not all resin is epoxy — and the choice that matters is depth. Buy a coating epoxy for anything up to 1/8 in in one go: flood coats, bar tops, tumblers. Buy a casting epoxy for pours up to 2 in: river tables, molds, coasters. Buy UV resin only for jewelry-sized work, because light will not cure through anything thicker than a coin. Polyester and polyurethane resins are for repair and production casting and are not what a craft project wants.
"Resin" is a category, not a product. Epoxy is one kind of resin — the kind almost every craft project means — and even inside epoxy there are two systems that behave so differently that using one for the other's job does not work at all. Then there are polyester and polyurethane resins, which are genuinely different chemistries sold in the same aisle, and UV resin, which is a different thing again.
The good news is that one question sorts almost all of it. How deep is the resin going to be at its thickest point? A coating epoxy is formulated to be poured 1/8 in at a time and cure fast; a casting epoxy is formulated to react slowly enough that 2 in of it can shed its own heat. Everything else about them — the ratio, the working time, the cure — follows from that one design decision.
The bad news is that the labels do not make it obvious, and the consequence of choosing wrong is not a slower cure. A casting-depth pour of a coating epoxy gets hot enough to crack the piece and scorch the surface underneath it. The pour depth guide goes into that properly; the calculator checks your depth against whichever system you have picked.
The four things that actually differ
Every figure in the top three rows comes off that system's own row in this site's data, so the calculator and this table cannot disagree. The bottom rows are not craft resins and have no depth or cure figure here on purpose — this is a comparison table, not a recommendation.
Buy by the depth you are pouring
An eighth of an inch per flood coat. That is not a suggestion about finish quality — a table top system reaches its peak reaction temperature in twenty minutes or so, and depth is what decides whether that heat can escape into the room or stays trapped in the middle of the pour. Build up thickness with several coats, letting each one firm up first. A bar top flood coat, 8 ft takes about 5.2 litres in a single flood coat. Mixed 1:1, handled in 24 hours, hard in 3 days.
The trade is speed for depth, and it is a real trade: 7 days to full cure against 3 days. Coasters, set of 8 at 10 mm is one pour of 691 ml here, and 4 separate coats over several days in a coating epoxy.
No hardener, nothing to measure, and set in about a minute. Its limit is optical rather than thermal — the resin absorbs the light that cures it, so anything thicker skins on top and stays liquid underneath forever. The UV resin guide covers where the line falls.
What the differences actually come from
A resin that cures fast releases its heat fast, and heat trapped in a deep mass runs away with itself. So a coating epoxy is quick and shallow by design and a casting epoxy is slow and deep by design. There is no product that is both, and a brand claiming one is quoting a figure at some depth you should go and find.
Table top systems are usually 1:1 and deep pour ones 2:1 — because the hardener does a different job in each, not because one is easier to measure. And a ratio quoted by volume is not the same number by weight: resin is 1.1 g/ml against hardener's 1, so 2:1 by volume is 2.20:1 on a scale. The mix ratio calculator converts it.
Casting epoxy is thinner and has hours to work in, so bubbles rise and clear on their own. Coating epoxy is thicker and sets in under an hour, which is why every tutorial for it involves a torch. If you are working with something bubble-prone and thick, that is the resin talking, not your technique.
Almost everything looks clear on the day. What separates the products is what happens after a year in a sunlit room: a good coating epoxy with UV inhibitors holds up, UV resin yellows noticeably sooner, and polyester yellows fastest of all. If a piece is going to be sold or kept, that is worth paying for.
Polyester / fibreglass resin turns up constantly because it is cheap and because the fibreglass trade is enormous. It smells powerfully of styrene, needs real respiratory protection rather than an open window, shrinks as it cures, yellows quickly and stays slightly flexible. It is genuinely cheaper than epoxy, which is why it turns up in casting kits, and it is the wrong material for anything that has to stay clear or be handled indoors. If a page is talking about lay-up, chopped strand mat or gel coat, it is about boat repair — a different craft with different rules, and not this site.
Choosing without wasting a kit
The exotherm does not care that most of the piece is thin. A river table with a 45 mm channel is a 45 mm pour even though the slabs either side are only being skimmed. Pick the system for the deepest part.
Every serious brand publishes one, and it states the maximum pour depth, the ratio and whether the ratio is by volume or by weight. Those three facts are the only ones that decide whether the kit will work for you, and they are precisely the three the front of the bottle tends not to say.
Resins differ between brands in ways that matter — viscosity, working time, how they behave with your pigment. A quart-sized kit is enough to find out whether you like one before you commit to a gallon of it.
"Casting resin" is used for epoxy, polyester and polyurethane interchangeably. The one you want for clear craft work is epoxy. If the listing mentions a catalyst measured in drops, or a working time of two minutes, or a strong smell, it is one of the others.
A coating epoxy is still a coating epoxy — use it for flood coats and buy a casting resin for the deep work. What does not work is trying to make it do the other job by pouring slowly or leaving it longer. The calculator will tell you how many coats your depth would need.
Check your depth against the resin you have
Pick your system and your project, and the calculator gives the volume, the resin and hardener split, and how many separate pours that depth needs — with a warning if it is past what your resin can take in one go.
Open the epoxy calculator →Print the pour-depth card
Maximum pour depth and cure windows by resin type — the number that cracks a casting. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.