Here is a list of some materials and whether they are conductors or insulators of Hieronymus' Eloptic Energy. He believed that this is the energy flowing in the wires in the "Grow Plants in the Dark" experiment, and in all of the machines he invented. Note that wood is a special material, and may be a necessary material for the light boxes in the plants experiment.

Eloptic Current Conductors: all metals, brown bakelite, natural black rubber

Eloptic wave conductors: glass of many types but not leaded, air, paper, magnetic field lines (may not be a conductor but a deflector), sunlight, strong long-tube fluorescent lighting.

Eloptic semiconductors: wood which has a short memory (storage) capacity

Eloptic Insulators: black bakelite (McMaster Carr Garolite Grade XX paper reinforced is great), thin polypropylene baggies, black enamel varnish, vinyl tape and wire insulation.

Eloptic Energy storage: wood (1-5 minutes before it dies out), water, sugar, milk, vodka (those 4 store nearly indefinitely if kept from sunlight and magnetic fields)

Eloptic Amplifiers: chemical types (I never tried them), vacuum tubes like 9001, transistor like CK722, N-FET transistors like 2N5670.