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Naval Research Laboratory sent a pizza box–size “sandwich panel” into orbit with solar cells on one side, a filling of electronics, and microwave transmitters on the other side to demonstrate sunlight-to-microwave conversion.

Next year, however, the Air Force plans to test a sandwich panel that will beam its energy down.

Erlicher explained how large refrigeration storage chambers above ground use a “sandwich panel” insulated with polyurethane and sheets of metal to keep the inside cool.

In the underground caves, the rocks act as the "sandwich panel", so it is "as natural as possible"