Are these materials safe to use?

Article courtesy of Smooth-On, Inc.

Smooth-On materials should be handled with the same care you use when handling household cleaning products. Common sense should rule the day. For example, you would not want your children to use these materials.

  • Our liquid rubbers, plastics, foams, release agents, etc. are safe to use if directions are read and followed carefully. Not respecting these chemicals and exercising caution when using them can result in a trip to the hospital (see "sensitization" below).
  • Do not use these materials in your home. Use them in your garage, dedicated workshop or basement with good ventilation. Keep children and pets away while using these materials.
  • Before using any material, read and understand the technical bulletin and Safety Data Sheet for the product you are using. Find the technical bulletin and SDS for any Smooth-On product here.
  • There are different health risks associated with different materials. Do not assume that because you are familiar with one material that the same handling procedures apply to a different material.

Protect Yourself

You should wear long sleeve garments and disposable gloves to minimize skin contact. Safety goggles will protect your eyes in the event that inadvertent splashing of a material occurs.

Skin Contact? Lightly wipe affected area immediately with solvent and then wash thoroughly with soap and water.

Eye Contact? If contaminated, flush eyes with water for 15 minutes and seek immediate medical attention.


Avoid breathing in plaster dust, mist from aerosol sprayers or fumes of any kind, etc. When using any material associated with mold making and casting, you must have "room size" ventilation (400 ft² / 38 m²) or greater.

If using these materials on a regular basis, you should install an external ventilation system in your workshop and use all materials in proximity to the working vent. Wearing a NIOSH-approved respirator will further minimize risk of inhalation.

Spraying Material? If you are spraying rubber, plastics or foams, try to do your spraying outdoors in an open space. Regardless of spraying outdoors or inside, anyone in the spray area must wear a NIOSH-approved respirator and disposable gloves at the very least.

Using Aliphatic Isocyanates

There is a class of polyurethane chemistry known as "aliphatic isocyantes" that require extra handling precautions. These are for "industrial use" only and should not be used by students, hobbyists, etc.

Which Smooth-On Products Are Aliphatic Isocyanates?

  • Any Crystal Clear™ liquid plastic product.
  • SMASH!™ Plastic
  • Clear Flex™ 50 & 95 urethane rubber
  • TASK™ 12 plastic
  • Simpact™ 80 urethane

If using one of these products, you must wear a NIOSH-approved respirator, long sleeve garments and disposable gloves to avoid skin contact.


If you are having an allergic reaction while using polyurethanes, stop using them and seek immediate medical attention.

Symptoms Include: if you are having trouble breathing, experiencing throat discomfort, itching eyes, and/or a skin rash, you may be having a reaction to these materials.

Cease and Desist – Permanently! If you experience these symptoms following any exposure to a urethane product, chances are you have become sensitized and you will experience a reaction every time. At this point, you should avoid using urethanes.


This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.