Why is gypsum unique?

• A. It has a high water content that absorbs a great deal of heat as the moisture evaporates
• B. It is the lightest building material
• C. It conducts electricity
• D. It is impermeable

Answer: (A)

Gypsum’s standout property is its water content that absorbs heat as the moisture evaporates. When gypsum is heated, the water bound in the mineral is released in an endothermic dehydration reaction. This takes in a substantial amount of heat, which slows the temperature rise in what's behind the gypsum and buys time in a fire scenario, contributing to its fire-resistance role in drywall and other gypsum-based products.

Other statements don’t fit because gypsum is not the lightest building material, it does not conduct electricity (it’s a poor conductor and acts as an insulator), and it is not completely impermeable to moisture.