All materials except Wall, (including Rigid, Rigid Axis, and Elastic) are a form of fluid when enough loose particles are collected. For example, a large collection of loose Tensile+Rigid particles will behave just like Tensile.

Fluids are one of the things the OE-Cake physics engine simulates best.

Non-fluid materials will only behave as expected immediately after being drawn, and loose particles cannot be turned back into a solid.