Low Viscosity, Easy To Use Resin offering tremendous versatility and economy. Perfect for casting detailed models, prototypes, props and cast effect pieces.

TheSmooth-Cast 300 Seriesof liquid plastics are ultra-low viscosity casting resins that yield castings that arebright white and virtually bubble free. Vacuum degassing is not necessary. They offer the convenience of a 1A:1B by volume or 100A:90B by weight mix ratio. The differences between them are pot life and demold time.

These resins readily accept fillers and can be colored with Smooth-On color tints. Fully cured castings are tough, durable, machinable and paintable. They resist moisture and mild solvents. Applications include reproducing small to medium size sculptures, making prototype models, special effect props and decorative jewelry.


  • Easy to measure and mix- 1:1 mix ratio by volume - no scale required
  • Low viscosity- captures excellent detail - no degassing necessary
  • Resin cures to abright whitefinish

Safety- Materials should be stored and used in a warm environment (73 F / 23 C). These products have a limited shelf life and should be used as soon as possible. All liquid urethanes are??moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic. Mixing should be done in a well-ventilated area. Wear safety glasses, long sleeves, and rubber gloves to minimize contamination risk. Because no two applications are quite the same, a small test application to determine suitability for your project is recommended if theperformance of this material is in question.

Applying A Release Agent- A release agent is necessary to facilitate demolding when casting into or over most surfaces. Use a release agent made specifically for mold making . A liberal coat of release agent should be applied on to all surfaces that will contact the plastic.

IMPORTANT:To ensure thorough coverage, apply release and brush with a soft brush over all surfaces. Follow with a light mist coating and let the release agent dry for 30 minutes. Smooth-On silicone rubber molds usually do not require a release agent unless casting silicone into the mold. Applying a release agent will prolong the life of the mold.

MEASURING & MIXING... Liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic. Materials should be stored and used in a warm environment (73F/23C).

Stir or shake both Part A & Part B thoroughly before dispensing. After dispensing equal amounts of Parts A and B into mixing container (100A:90B by weight) and mixthoroughly. Stir deliberately making sure that you scrape the sides and bottom of the mixing container several times. Be careful not to splash low viscosity material out of the container.


Pouring- Pour your mixture in a single spot at the lowest point of the containment field and let the mixture seek its level. This will help minimize air entrapment.

For Best Results. . . Best results are obtained using a pressure casting technique. After pouring the mixed compound, the entire casting assembly (mold, dam structure, etc.) is placed in a pressure chamber and subjected to 60 PSI (4.2 kg/cm2) air pressure for the full cure time of the material.

Curing- Warning: Fumes, which may be visible as this product starts to gel and cure, will dissipate with adequate ventilation. Only use this product with room size ventilation and do not inhale/breathe fumes. Castings will be extremely hot immediately following cure and may burn the skin. Let cool to room temperature before handling. Smooth-Cast 300 will cure in 7 - 10 minutes depending on mass and mold configuration.

Post Cure- Castings will reach full cure faster and achieve maximum physical properties if post cured. Allow material to cure for recommended Cure Time at room temperature followed by 4 - 6 hours at 150F/65C. Allow casting to come to room temperature before handling.

Performance- Cured castings are rigid and durable. They resist moisture, moderate heat, solvents, dilute acids and can be machined, primed/ painted or bonded to other surfaces (any release agent must be removed). If machining cured material, wear dust mask or other apparatus to prevent inhalation of residual particles. Castings can be displayed outdoors after priming and painting. Unpainted castings will yellow over time - more quickly when exposed to ultra-violet light.

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