Best resin molds
Sorted by what you are making rather than by brand, and every one with the number listings never print: how much resin a cavity actually holds.
Buy by what you are casting and by the depth it needs. Coaster and tray molds are 79 ml cavities that want a casting resin, not the coating epoxy most kits include. Jewelry molds are 3 ml and shallow enough for UV resin. Deep and geometric molds need firmer silicone and more than one pour. The two things that separate a good mold from a bad one are a glossy surface — a matt mold casts a matt piece that then has to be sanded clear — and silicone firm enough not to bulge under the weight of what is in it.
Almost every resin mold listing tells you the same things: that it is food-grade silicone, that it is reusable, and that it is easy to demold. Almost none of them tell you the two things that decide whether it is any good, and none at all reliably tell you the one number you need before you can mix anything — how much resin a cavity actually holds.
That number is the reason this page exists. A four-cavity round coaster mold takes about 346 ml of mixed resin to fill, including the 10% that stays in the cup. A serving tray takes 528 ml in one go, which is the pour where running short is unrecoverable. Every figure in the table below is worked out from the mold's own dimensions using the same function the calculator runs on, so you can substitute your own and get the right answer.
The other thing worth settling before you buy: most beginner kits pair a coating epoxy with molds that are a casting depth. 10 mm of resin is well past what table top / coating epoxy will take in one pour, so the kit's own molds need 4 separate coats or a different resin. Which type to buy covers that properly, and the beginner's guide the rest of a first pour.
Every mold, and what it takes to fill
Cavity volumes are derived from each mold's dimensions rather than taken from a listing. "To fill" is every cavity plus 10% wastage — what you actually mix, not what the mold holds. The resin column is the system that depth needs, which for most of this list is not the one in a beginner kit.
What separates a good mold from a cheap one
This is the single biggest quality difference and it is almost never in the listing. Silicone casts whatever surface it has: a polished mold gives a piece that comes out clear and needs nothing doing to it, and a matt mold gives a frosted piece that has to be sanded through several grits and polished back. If a product photo shows cloudy castings, that is the mold, not the resin.
Softer silicone releases a piece with undercuts easily and flexes under load, so a deep cavity bulges and casts a barrel instead of a cube. Firmer silicone holds its edges and fights you on release. Small jewelry molds want the soft end; trays and deep blocks want the firm end, because they are holding 900 ml of liquid that is trying to spread the walls.
A thin-walled mold on an uneven surface casts a wedge, and you will not notice until it has cured. Thicker walls hold the shape and hold heat, which is a mixed blessing — good for a slow even cure, bad for a deep pour that is already fighting its own exotherm. Check that the base is flat by putting it on glass, before you fill it rather than after.
What to buy for what you are casting
The commonest first purchase and the commonest first mistake. A 10 mm coaster is a casting: 4 coats of table top / coating epoxy over as many days, or one pour of deep pour / casting epoxy. A four-cavity round mold takes 346 ml to fill; a six-cavity square one takes 660 ml, because square cavities hold about a quarter more than round ones of the same width. The coaster guide covers the build.
A 3 mm pendant cavity is inside what a lamp will cure, which is why so much small jewelry is made with uv resin — a tray of twelve is finished in an evening rather than three days. These want soft silicone, because a cured pendant with an undercut has to flex out rather than be pulled. The UV resin guide covers where the depth limit falls, and the jewelry guide the rest.
A sphere is the worst shape there is for an exotherm: the middle is as far from any surface as geometry allows, and silicone insulates it further. Flat-faced shapes are the other problem, because a flat face shows every flaw in the mold surface — this is the category where a polished mold genuinely earns its price rather than just looking nicer.
A 60 mm casting block is 2 lifts of deep pour / casting epoxy whatever the bottle says, because 2 3/8 in is past a single lift. It also holds 900 ml in one cavity, which is a lot of mass to be curing inside an insulating material. The pour depth guide explains why that matters.
A 3 mm flat sheet is the only mold on this list table top / coating epoxy handles in one pour, and it takes 198 ml to fill. Cast the sheet, then cut, drill and sand shapes out of it — far cheaper per piece than buying a mold for every shape, and the offcuts go back in the next pour as inclusions.
Silicone molds are reusable and get better for a few castings as they season, then gradually cloud as the surface picks up micro-scratches — a hundred pours is a reasonable life for a well-treated one. Single-use plastic or acrylic forms exist for river tables and one-off shapes, and are taped and sealed rather than demolded. Do not use a mold made for candles, plaster or soap: they are frequently the wrong plastic and epoxy sticks to them.
Buying and looking after them
The two purchases go together and the mold decides the resin. A mold whose cavity volume is not stated can be measured in a minute with water and a jug — fill a cavity, pour it into the jug, and that is the number. The calculator takes it directly.
Epoxy does not stick to silicone, so a release agent is solving a problem you do not have — and the aerosol ones leave a film that shows on the casting. If a piece will not come out, the mold is too firm or the piece has an undercut, and the fix is to freeze it for twenty minutes and try again.
A sweeping pass above the surface is fine and is how you get the bubbles out. Resting the flame on the mold melts the surface permanently, and from then on every casting carries that mark. Keep the flame moving and keep it above the resin.
Cured drips peel off silicone with a fingernail. Solvent attacks the surface and dulls it, which is the one thing you are paying for. Warm soapy water and a soft cloth, and store them flat rather than stacked — a mold stored under something heavy casts that shape for months.
Resin self-levels to the horizon, not to the mold, so a mold sitting on a millimetre of tilt casts a wedge and you cannot fix it afterwards. Put a small spirit level in the cavity before anything is mixed. A shim of card under one corner is usually all it takes.
Mixing a small batch accurately is harder than mixing a large one, so casting four coasters at once is more repeatable than casting one four times — and the marginal cost of filling a spare cavity is small against the cost of a batch that did not cure.
Work out what your mold takes
Enter a cavity volume and how many you are filling, or the dimensions if the listing does not say, and the calculator gives what to mix, the resin and hardener split, and whether the depth needs more than one pour.
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.