If you have stood in front of a wall of UV resin bottles labeled “hard,” “soft,” and “gel” and wondered which one you actually need, the short version is this: hard is your default, soft is for flex, and gel is for height. They are not quality grades where one is the “good” bottle and the others are compromises — they are three formulations tuned for three different jobs. The numbers in the comparison table below tell the whole story: the types differ almost entirely in two measurable properties, cured hardness (measured on the Shore scale) and viscosity (measured in centipoise, or cps). Everything else — cure time, shrinkage, clarity, the hard depth limit — is roughly the same across all three.
Here is the 30-second answer. If you only buy one bottle, buy a hard type at around 85D Shore D and roughly 2000 cps. It is the do-everything resin: it casts in molds, fills bezels, light-domes a flat pendant, and coats flat artwork, all from one bottle, finishing rigid and glass-clear. Buy a soft type (around 15D Shore D) on top of that only when you make pieces that have to bend without snapping — open bezels, bracelet links, ring bands, thin dangling charms, phone-grip accents. Buy a gel or high-viscosity type (5000-6000 cps, curing up to about 90D) only when you need to build height that will not run off the edge — domes, 3D petals, water-drop effects, raised lettering. That is the entire decision.
How the three types actually differ: hardness and viscosity, not quality
When manufacturers split a UV resin line into hard, soft, and gel, they are changing the formula along two axes. The first is how hard the resin cures, expressed as a Shore durometer number. A hard type lands around 85D Shore D — rigid, scratch-resistant, glass-like, the kind of surface that resists a fingernail. A soft type drops dramatically to about 15D Shore D (Let’s Resin publishes this figure for its soft type), which is soft enough that a thin cured piece flexes and springs back instead of cracking. Some flexible products are instead rated on the softer 25A scale, which is a different durometer scale entirely and not directly comparable — worth knowing when you compare spec sheets across brands.
The second axis is viscosity, or how thick the liquid resin is before you cure it. A hard type sits at a medium ~2000 cps: thin enough to self-level into a smooth coat, but thick enough to hold a modest dome before you flip on the lamp. A soft type is generally low-viscosity and self-leveling. A gel or high-viscosity type is the outlier at roughly 5000-6000 cps — thick like cold syrup, slow to flow, and content to stay piled up on a curve or a vertical edge. That thickness is the entire point: it is what lets gel resin build shapes that thinner resins simply run away from.
Two properties barely move across all three. Cured shrinkage stays under 2% for every type, and — critically — every UV resin type cures only about 2-4 mm deep per pass. Hold those two facts; they govern more of your real-world results than the type label does.
Hard type (~85D, ~2000 cps): the do-everything default
If a project does not specifically demand flex or height, reach for the hard type. At about 85D Shore D it cures to a rigid, scratch-resistant, glass-clear surface that holds up to handling, and its ~2000 cps body is the Goldilocks viscosity: it self-levels well enough to coat flat artwork or sealed polymer clay, yet has enough body to hold a light dome on a small pendant. It casts cleanly in detail molds, flows into bezels, and seals porous craft surfaces. Under a standard 36W lamp at 365-405nm it cures a thin layer in 3-5 minutes, and because it only reacts to UV, you have effectively unlimited working time in the bottle to position inclusions before you commit to curing.
The Let’s Resin Hard Type 2.0 and JDiction Hard Type are the obvious workhorses here; the JDiction even cures a touch faster (2-4 minutes under 36W) and will set up in strong sunlight, which is handy if you are caught without a lamp. The trade-offs are exactly what you would expect from a rigid resin: it cracks on anything that needs to flex, and its medium viscosity will run off the edges of a tall dome. For those two jobs you switch types — which is the whole reason soft and gel exist.
Soft type (~15D / 25A): for pieces that must bend
A soft type is a single-purpose tool, and that purpose is flex. At about 15D Shore D it cures bendable and elastic, so thin pieces — keychains, charms, fabric-embedded crafts, phone-case accents, soft jewelry that moves with the body — flex and recover instead of snapping the first time they are stressed. In jewelry specifically, soft type is what you want for open-back bracelet links, ring bands, and thin dangling charms, where a rigid 85D resin would crack at the first sharp knock. It cures just as fast as a hard type (3-5 minutes under UV) and shares the same sub-2% shrinkage and crystal-clear, yellowing-resistant finish.
The price of that flexibility is durability. A soft type dents and scratches easily, so it is wrong for a rigid showpiece pendant or a domed cabochon. Its surface can stay slightly tackier, which means it attracts dust more readily before and after cure. And the Let’s Resin Soft Type ships in a smaller 100g bottle, so it costs more per gram — fine, because you only use it where flex is genuinely required, not as your bulk resin.
Gel / high-viscosity (5000-6000 cps, up to ~90D): for building height
Gel resin solves the one problem thin resin cannot: keeping a build standing up. At roughly 5000-6000 cps it is thick and slow-flowing, so when you pile it into a dome on a flat pendant or sculpt a 3D petal, surface tension holds the shape on the curve instead of letting it slump over the edge. It is the resin for water-drop effects and raised lettering, and despite its thickness it cures to the highest hardness in the lineup — up to about 90D Shore D — so the finished build is genuinely scratch-resistant. The slow flow is also a quiet bonus: you get extra working time to nudge inclusions into place before curing.
What gel cannot do is lie down flat. It is too thick to self-level into a clean smooth coat, awkward to work into fine bezels and small detail molds, and trapped bubbles rise out of it slowly, so you have to be patient or use a torch pass. Brands handle this with dedicated products: the Let’s Resin High Viscosity Thick UV Resin and JDiction’s high-viscosity 300g variant are both built for doming, while Padico splits the job across Sky Drop (low-viscosity for molds and bezels) and Moon Drop (slightly high-viscosity for domes). See the specs below for how the viscosities line up.
Which type for jewelry vs coating vs molds
Route by the job, not the brand. For coating flat artwork or sealing clay, a hard type’s ~2000 cps flows out into the smoothest self-leveling film. For a raised dome on top of that same flat piece, switch to a gel at 5000-6000 cps and build the dome in stacked thin layers. For mold casting and bezel fill, a hard or low-viscosity type flows into detail best. For jewelry, default to hard for pendants, earrings, and cabochons, and only reach for soft on the bend-or-break pieces. Our best resin equipment buyer’s guide walks through the lamps and tools that make each of these jobs cleaner, and you can browse every head-to-head in the comparisons hub.
The brands: Let’s Resin, JDiction, and premium Padico
Let’s Resin and JDiction are the budget-friendly bulk craft brands, and both split their lines into hard, soft, and high-viscosity options — Let’s Resin publishes the most explicit numeric specs (the 85D, 15D, and ~2000/5000-6000 cps figures all come from its own product spec sheets). JDiction trades some published precision for fast cure times, solar-curing, and beginner-friendly lamp bundles. Padico is the premium Japanese tier and the clearest illustration that the type split is universal: its Star Drop is the hard type, Star Drop Soft is the flexible type, and Star Drop Gummy is a bouncy jelly type, with Sky Drop (low-viscosity) and Moon Drop (high-viscosity) rounding out the family. Padico also cures under a low-watt 6-9W UV-LED or plain sunlight in 30-90 seconds, versus 2-4 minutes under a 36W lamp — the trade is small 25g/70g bottles at a much higher cost per gram, which is why it lives in the fine-detail and kawaii-charm niche.
The 2-4 mm rule that overrides every type choice
This is the single most important fact on the page, and it applies equally to hard, soft, and gel: UV light only penetrates about 2-4 mm into resin before it runs out of energy. Pour thicker than that and the bottom stays sticky and uncured no matter how long you run the lamp — and doubling your usable cure depth takes roughly a tenfold jump in UV intensity, which is why a brighter lamp is not a real fix. The working rule is to pour and fully cure thin layers, about 2-4 mm each, and stack them to build any real depth. If your casting is deeper than a fingernail, stop reaching for UV resin entirely and use a two-part epoxy, which cures chemically all the way through regardless of thickness. No type label changes this; it is physics, not formulation.
Safety: none of these are food-safe
A conservative, important note: no standard consumer UV resin — hard, soft, or gel — is tested or FDA-certified for direct food contact. Even fully cured, these resins can release small amounts of chemicals under heat, acidic or fatty foods, or repeated washing, and uncured resin of any type is toxic and a skin sensitizer. Keep all three away from cup rims, plates, coasters that hold food, and anything that touches food or drink, and use a certified food-contact epoxy for those projects instead. When working with any type, wear nitrile gloves, ventilate the space, and never stare into the curing lamp — UV exposure is a real hazard to your eyes and skin.
Verdict
Buy the hard type first and use it for almost everything. Add a soft type when you make pieces that must bend, and a gel / high-viscosity type when you need to build height that will not run off the edge. The three are tuned for three jobs, not ranked best to worst — and whichever you reach for, respect the 2-4 mm cure-depth limit and keep all of them away from food. See the comparison table and specs below for the exact hardness, viscosity, and cure figures behind each pick.