Did you not notice that vpt sort of gave the answer above, but for the special case of non-reversible so similar to the phase change.
The magic word is 'anisotropy'. Certain types of rubber and plastic exhibit the property reversibly.
Imagine a tray full of coil springs all aligned in the same direction with their coils partially fitting into each other. If they are heated they expand and elongate, but sideways each coil just moves slightly deeper into the next spring so no bulk expansion takes place in that direction. You can make a plastic that does this on a molecular level. Then if you form the plastic into a ring with the springs oriented radially heating it can produce both an increase in the external diameter and a reduction on internal diameter at the same time.