Artists have the options of polyester and polyurethane resins when it is time to do clay modeling and casting. These resins are good for such work due to their ability to cure and form a hard cast. They will also produce the clearness of glass, and have a high gloss finish after proper sanding and buffing. You however need to know which one applies in a particular job. To make a better choice, you need to know how different these resins are.
Polyester resins are the cheaper alternatives in the market. It needs there to be a catalyst or an accelerator for it to work well. They on the other hand give off a toxic odor, which forces an artist to wear a protective gas mask as long as they are casting. You also need to work in a properly ventilated studio. It then needs reinforcement in the form of a filler, such as fiberglass. In future you can expect them to develop spider web-like cracks.
Polyester resins will also cure to a crystal clear finish. There is however the danger of them yellowing out with time, when they are struck by UV light. Since they dry fast, they need an artist to finish up quickly. When ten minutes are up, they shall become useless. They also have a high and unpredictable shrinkage rate, which adds to the difficulty of handling them. IT makes for a good bond between fiberglass fabrics.
Polyurethane resins, on the other hand, are more costly. They however have more uses to them. They have found work in rubbers, plastics, inks, medicines, and more. They last longer and resist the effects of chemicals, oils, grease, and abrasion much better. When casting, they will not emit any harmful toxic gases.
You can get them in opaque and water clear resins. The costs they form will come with a lot of details and will not tear so easily. You can use it to make a wider variety of plastics, from the softest to the hardest. Since they can easily form bubbles, you need to work on them in a pressure pot or a vacuum chamber. You need to also invest in special paint to work on them. You thus have more limited color options to work with.
This material is however highly sensitive to moisture. You need to have the right climate to cure it. If you work in a humid environment, you should make use of a dehumidifier. It is therefore good that they cure faster. You thus need to move fast in your working.
These are the things that make you realize that polyurethane resins are better for general mold making and casting works. They are the number one material in a clay studio. Polyester on the other hand is best for fiberglass fabrications.