Welcome to our Frequently Asked Questions page! Browse our FAQ to find answers to commonly asked questions about our products. Our team of experts has compiled this comprehensive list to help you achieve success with our products.  

Ratios—Do I need to measure by weight or by volume?

Silicone RTVs
Our systems are formulated to achieve the best physical properties by weight. However, most Silpak’s systems are flexible enough to mix by volume. For mix ratios other than 1A:1B, the use of a scale is highly recommended.  

Urethane Plastics & Urethane RTVs
Most Silpak products can be measured by volume. However, measuring by weight is typically more accurate. For mix ratios other than 1A:1B, the use of a scale is highly recommended.

How does temperature affect material?

Cold temperatures do affect the cure of silicones, more with the platinum series since it cures quicker with heat and stops curing with freezing temperatures. Tin based silicones are not heat curable and will cure in cooler temperatures. The first hour of cure (Tin based) will effect the final time the silicone cures. Very dry or low humidity will also slow the curing process. Do not try to heat-cure the Tin based silicones. Adding more catalyst will cure Tin based silicones and some Platinum based silicones quicker; although, this will affect the physical properties and the library shelf life. Platinum silicones will cure faster with each degree of temperature over 90F (Not recommended to cure by elevated temperatures unless pre-tested). Heat saturation for depth of rubber thickness needs to be factored in for final cure of silicone—add 1 hour for each 1” thickness.

Urethane Plastics and Urethane RTVs

Urethane materials cure best when the temperature of the material is between 70F – 80F. As the material becomes warmer it will react and cure quicker, and when it is cooler the cure process is slowed—if too cold, a non-cure of material could result. The temperature of the mold and master tool can also affect the cure process.

What to do if material freezes?

Urethane Plastics and Foams
Warm in a hot water bath before using. Hot tap water is recommended.

Urethane RTVs

Warm in a hot water bath before using. Hot tap water is recommended.

Silicone RTVs
Warm in a hot water bath before using. Hot tap water is recommended.

DO NOT ALLOW TO FREEZE. Freezing makes latex unusable.  

How should materials be stored?

For best results, store liquid products indoors at temperatures between 60°F and 95°F. Long-term exposure to temperatures below and above this range may cause the product to perform improperly. Polyurethane products should always be at room temperature before use.

What can I do if I get moisture contamination in urethane resin?

Add some BAYLITH L MB (moisture scavenger) to the B side or vacuum B side for 1 hour and test.

How can I warm materials or molds?

The safest way to heat up cold materials is in a hot water bath. Hot tap water works well. The material container can be placed directly in a plastic trash bag and sealed off to avoid moisture contamination. Large tools and molds can be heated by using an electric heating blanket.

How do I know when the material is too old to use?

The first noticeable change is the condition of the base--a gain in viscosity (thickness), formation of chunks or crystals, unusual color change. A small test batch can be mixed and cured to establish conditions. Some materials can be salvaged while others should be turned into a solid waste and disposed of in the trash.

How can I prevent getting bubbles in my finished part?

Urethane Plastic
Air can adhere to the surface. Dust the mold surface with Prolite FR 50 or a dry talc powder. Cast parts under pressure in a pressure pot between 60 – 80psi.

How should I mix the material to avoid bubbles?

Mix by hand with a tongue depressor or Jiffy mixer for larger mixes. Stir gently, moving in a figure 8, being careful not to whip air into the mix. Be sure to scrape the sides and bottom of the container while mixing. Pour gently as well to minimize turbulence that may be created by the pouring action.

What should I do when the material does not cure properly?

After you’ve checked material age, mix ratio accuracy, accounted for ambient curing temperature of material, contact Silpak and ask for Technical Support.

What if the material is curing too fast?

Urethane Plastic
In warm summer heat, cool the A side to 50F – 60F in the refrigerator for 30 minutes before using. Cooling both sides can result in poorly cured parts.


In hot summer weather, cool A side in refrigerator. Reduce the catalyst ratio, i.e. a mix ratio of 10% down to 9%. Mixing smaller batches and pouring several layers will allow the air to surface quicker.

Can silicone be used without the use of a vacuum chamber?

Silicone can be used without the use of a vacuum chamber. Brush on the surface coat using forced air to work out any surface air. Back fill 30 minutes later. When pouring rubber into the cavity, pour thin streams of mixed material from high above the surface into the corner of the mold, allowing the rubber to roll out, pushing air away as it fills the mold cavity. Curing a mold while under pressure at 50-60 psi also works well in providing strong, bubble free molds. After pouring mold, place it in a leak-free Pressure Pot, and allow it to remain until cured. Air compressor should always be larger than the pressure pot used.