Flubber is an example of matter because it is a physical substance (solid) that occupies space.
Flubber is a gelatinous rubbery polymer that is produced by cross-linking a boron compound with polyvinyl alcohol (PVA).
A matter is any physical substance that occupies space and has inertia. Matter is composed of many types of particles that have mass and sizes and it can exist in different states such as solid, liquid and gas.