Double glass walls and freezer: what they have in common

1. Step 1. Double glass walls — is part of — Dewar flask. Two bulbs, one inside the other.
2. Step 2. Dewar flask — evolved into — Vacuum flask. A household Dewar flask.
3. Step 3. Vacuum flask — uses — Thermal insulation. Insulation.
4. Step 4. Thermal insulation — is part of — Freezer. Polyurethane foam in the walls.

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