Mass

Overview
 of a material determines how much each block weighs.

Use
is used together with Max Load to calculate Structural Integrity and therefor planning structures of any sort.

To do this, divide Max Load by Mass of the block and round down the quotient. Structural Integrity = RoundDown( Max Load ÷ Mass ) 

Video Tutorial (Outdated)
The video below explains the physics of mass and max load for various building materials in detail.