Waterproof or not
Chemistry · Key Stage 1 · The School
Testing it
You want to know if a material is WATERPROOF. Drip a few drops of water on it. Then watch. Does the water sit on top in a bead? Or does it soak straight in and come through underneath? Test several materials the same way. Use the same amount of water each time. That is how you compare them fairly.
What keeps water out
Plastic keeps water out. So do rubber, waxed cloth and metal. Paper lets it through. So do cotton, wool and cardboard. That is why an umbrella is plastic or coated fabric, and not paper. It is why wellington boots are made of 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. So sensible clothing is layers of different materials. Each layer does one job.
Put one drop of water on foil. Then on kitchen paper. Then on a plastic bag. Then on a cotton sock. Wait one minute. Now look underneath each one. On foil and plastic the drop is still sitting on top. Nothing came through. Those are waterproof. On paper and cotton the drop spread out and went dark. The underside is wet. Those are not waterproof. Note that the water TOUCHED all four. Waterproof means it did not get through.