The thirty-second answer
If you are looking for a resin you pour into a mould and harden under a lamp, in seconds, for a 3D print, a craft piece, a pendant or a nail finish, you want a UV-curing resin and this is not that product.
If you are making FRP sheets, panels or mouldings that will sit in sunlight for years, and you want the finished part to resist yellowing, chalking and surface breakdown, then UV-stabilised resin is what you are after.
The two share two letters and nothing else. In a UV-curing resin, ultraviolet light is the energy source that makes it harden. In a UV-stabilised resin, ultraviolet light is the enemy the additives are there to defend against.
How UV-curing resin works
A UV-curing resin is a photopolymer. It contains a photoinitiator that absorbs light at a specific wavelength, usually around 365 to 405 nanometres, and splits into radicals that start polymerisation. Take the light away and the reaction stops essentially immediately.
That gives the properties those users want: indefinite working time in the dark, then cure on demand in seconds, with excellent detail resolution. It also gives the limitations: cure depth is limited by how far light penetrates, shadowed areas do not cure, and pigmented or filled formulations are difficult because the pigment blocks the very light needed for cure.
This is why UV-curing resins are used for thin layers and small parts, and why you will not find anyone laminating a roofing sheet with one.
How UV-stabilised polyester resin works
UV Stabilized Sheet Grade Yellow Resin is a conventional unsaturated polyester resin. It cures by free-radical copolymerisation of styrene with the polyester's double bonds, started by a peroxide catalyst, usually MEKP, with a cobalt accelerator that lets the peroxide decompose at room temperature.
No lamp is involved at any stage. Sunlight does not cure it, a UV lamp does not help it, and leaving it in the sun will do nothing useful. What decides cure is catalyst level, accelerator level and temperature. Cobalt-accelerated systems lose activity disproportionately below about fifteen degrees Celsius, which is the practical constraint in a cold workshop.
The UV part of the name describes what happens afterwards, in service. The resin carries a light-stabiliser package intended to slow the photo-oxidation that degrades polyester outdoors, and it is pre-pigmented so the colour is dispersed under factory control rather than stirred in on the shop floor.
Why the confusion is so common
Search behaviour is the main reason. UV resin as a search term is dominated by the craft and 3D-printing product, which sells in enormous volume in small bottles, so anyone typing those words tends to land in that world first.
Industrial buyers then arrive at a page selling a lamp-cured photopolymer and reasonably conclude either that it is the wrong supplier or, worse, that the two are interchangeable at different scales. They are not.
There is a second layer of confusion inside the industrial category itself. UV-resistant, UV-stabilised and weatherproof get used as if they meant the same thing. They do not, and the distinction is covered in the next section.
UV resistant, UV stabilised and weatherproof are three different claims
UV resistant properly describes polymers that are inherently stable in sunlight because of what they are made of. Acrylic, ASA, PVDF and PTFE are the usual examples. Their stability is structural rather than added.
UV stabilised means additives have been used to slow photo-oxidation in a polymer that is not inherently stable. Unsaturated polyester falls firmly in this group: its ester linkages and its polystyrene crosslinks are both photo-oxidisable, so any outdoor durability comes from the stabiliser package rather than from the backbone.
Weatherproof is a marketing word with no test behind it, and the same goes for UV proof. Neither should appear on a technical page. The defensible version of that claim names a weathering method, an exposure duration and a measured property retained, which is a very different sentence.
Which one do you actually need?
Ask what supplies the energy that hardens the material. If the answer is a lamp, you want a photopolymer and should look for a UV-curing product. If the answer is a catalyst you mix in, you want a conventional polyester and the UV in the name refers to service durability.
Then ask where the finished part lives. Indoors, permanently out of sunlight, and the stabiliser package is money spent on a property the part never uses; a standard sheet grade will serve. Outdoors for years, and the stabilisation is the point of the product.
Samrat Poly Resins does not supply a UV-curing or LED-curing resin. For decorative casting and clear art work, the epoxy casting and art grades are the relevant route and they are also conventionally cured rather than lamp cured.