Is there a way to improve surface finish when casting a rigid or flexible foam?

You can improve surface finish by applying back pressure.

Photo Examples:

Without applying back pressure, surface finish reveals open foam cells.

Drill holes into a board that can cover mold opening during casting.

Apply Ease Release®2831 to board. Pour foam into mold and place board over mold with holes centered over cavity.

Hold board firmly in place until foam stops rising. Let foam cure for 2 hours.

Use a scraping tool to remove excess foam.

Board is removed to reveal flat back of the casting.

Pressure uniformly compressed foam into mold detail resulting in better surface finish.

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.