Which of the following is listed as a common insulator?

• A. Dry wood
• B. Copper
• C. Water
• D. Brick

Answer: (A)

Insulators resist the transfer of heat (and electricity). Dry wood is a common insulator because its porous structure traps air, and air conducts heat very poorly. That keeps heat from moving through the material. Copper, being a metal, conducts heat and electricity well, so it’s not an insulator. Water conducts heat and electricity due to its dissolved ions and molecular movement, so it’s not an insulator either. Brick can slow heat transfer, but it doesn’t beat dry wood in typical insulator use. So dry wood best fits being listed as a common insulator.