Choosing a material from evidence
Chemistry · Key Stage 2 · The School
Saying a material is "best" is not a reason. Saying it conducted heat slowest in our test, so the handle stays cool, is. The tests from the last four lessons produce exactly this kind of statement, and it is what turns an opinion into evidence.
A lunchbox must be light, waterproof, rigid enough not to crush and safe with food. Plastic wins on all four. Glass is waterproof and rigid but heavy and breakable; card is light but not waterproof. The winner is the one with no disqualifying weakness, not the one that tops any single test.
Metal conducts heat, which is a problem for a handle and the whole point of a saucepan base. Glass is brittle, which is unacceptable in a football and fine in a window. Whether a property counts as good depends entirely on the job you are choosing for.
You may already know a coat keeps you warm. Testing fabrics for insulation still matters, because it replaces "everyone knows" with a measurement someone else could repeat and check. That is what makes the reason usable by another person.
A table with a row for each material and a column for each property turns four separate experiments into one thing you can read across. Somebody who was not there can look at it, see which material won on which test, and reach the same conclusion you did. Evidence that only makes sense to the person who collected it is not much use to anyone. A clear table fixes that on its own.