I am looking for "iso foam"; is this something that Smooth-On makes?

Yes, Smooth-On's Foam-iT! and FlexFoam-iT! series are both iso foam formulations, making them very high quality while being easy to use. These foams are also commonly referred to as "AB foams" in reference to their two-component (Part A & Part B) nature.

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.