Drill mixing (using a drill with mechanical mixer attachment, such as a "turbine" mixer) will introduce more air into the system, causing the foam to expand more. Below is an image showing the difference between drill mixing and hand mixing.
Does it matter whether I mix Foam-iT! or FlexFoam-iT! liquid castable foams by hand or use drill mixing?
Article courtesy of Smooth-On, Inc.
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.