I have a vacuum pump and chamber, but mostly use urethane rubber that I do not vacuum. Is there any advantage to vacuuming my urethane rubber before pouring?

Although urethane rubbers are low in viscosity and generally do not need to be vacuumed, they do contain air and you will benefit by vacuuming the urethane rubber.

General Rule: If you are fortunate enough to have a vacuum pump and chamber, use it for best results.

Disclaimer

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.