Choosing materials: properties and simple tests

Properties that decide a choice

Strength, flexibility, hardness, thermal conductivity, electrical conductivity, transparency and whether the material is waterproof. Engineers pick a material by listing the job first, then the properties that job needs.

Conductors and insulators of heat

Metals conduct heat well, which is why a metal spoon in hot soup gets hot along its whole length. Plastic and wood are thermal insulators, which is why handles are made of them. The same words are used for electricity, but a material can be good at one and not the other — always read which one the question means.

Testing a property fairly

To compare strength of paper types, hang the same weights on strips of the same width and length, and change only the paper. Without that, the result is about the strip, not the material.