Waterproof or not
Chemistry · Key Stage 1 · The School
Testing it
To find out whether a material is WATERPROOF, drip a few drops of water on it and watch. Does the water sit on top in a bead, or soak straight in and come through underneath? Testing several materials the same way, with the same amount of water, is how you compare them fairly.
What keeps water out
Plastic, rubber, waxed cloth and metal keep water out. Paper, cotton, wool and cardboard let it through. That is why an umbrella is plastic or coated fabric and not paper, and why wellington boots are rubber. The material was chosen for the job it has to do.
Choosing for the weather
On a rainy day you want waterproof things on the outside — a coat, boots, an umbrella. Underneath you want something warm, and warm materials like wool are usually not waterproof. Sensible clothing is layers of different materials, each doing one job.
Put one drop of water on each of foil, kitchen paper, a plastic bag and a cotton sock. Wait one minute, then look underneath. Foil and plastic: the drop is still sitting on top and nothing came through — waterproof. Paper and cotton: the drop spread out, went dark, and the underside is wet — not waterproof. Note that the water TOUCHED all four. Waterproof means it did not get through.