Medium-__ Fibreboard or Mdf, Building Wood
Puzzle 6 of Building a House Hard Pack
Question is: Medium-__ Fibreboard or Mdf, Building Wood
and the answer is: DENSITY
Word Meaning:
DENSITY — The amount of a certain phenomenon (such as stuff, things, energy, or otherwise) in a given area (surface area) or volume (amount of space).
Definitions from Wiktionary.