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Waterproof or Not?

Testing which materials let water through and which keep it out.

  • Define and explain Waterproof or Not? in your own words
  • Use key terms such as waterproof accurately
  • Apply what you have learned to new examples and questions
  • Avoid the common mistakes learners make with this topic

This lesson focuses on Waterproof or Not?: testing which materials let water through and which keep it out.

Definition: Waterproof or Not?

Testing which materials let water through and which keep it out.

Key ideas

Some materials let water or light through, others block them

A sponge soaks up water while a plastic bag keeps it out — one is absorbent and the other is waterproof. Clear glass is transparent, frosted glass is translucent, and wood is opaque. These blocking and letting-through properties decide how we use each material.

We choose materials to suit the job

Wellies are made of rubber because rubber is waterproof and bendy. Windows are made of glass because it is transparent and hard. Matching the property to the purpose is the key idea behind materials science, and engineers do it for everything from bridges to lunchboxes.

Key term — waterproof: Does not let water pass through it, like a plastic raincoat.

Which material for a raincoat?

Priya needs a material for a raincoat. She tests three: cotton fabric, plastic sheet and paper.

The raincoat must keep water out, so the material must be waterproof. Cotton soaks up water — it is absorbent, not waterproof. Paper tears and soaks through — no good either. The plastic sheet keeps water out and bends easily.

Answer: The plastic sheet — it is waterproof and flexible, the two properties a raincoat needs.

Common mistakes
  • Assuming shiny means waterproof Shininess is about light bouncing off the surface; a shiny sponge still soaks up water.
  • Saying 'material' when you mean 'object' The object is the chair; the material is the wood it is made from.

Practice

Why are umbrellas not made of paper?
What happens to paper in rain?

Paper is not waterproof — it soaks up water and tears, so it would fail as an umbrella.

Sort these into natural and man-made materials: wood, plastic, cotton, glass.
Natural materials come from plants, animals or rocks.

Natural: wood, cotton. Man-made: plastic, glass.

Name one transparent material and one opaque material.
Think of windows and walls.

Transparent: glass or clear plastic. Opaque: wood, metal or brick.

A material lets some light through but you cannot see through it clearly. What word describes it?
It sits between transparent and opaque.

Translucent.

Quick check

Waterproof or Not? — quick check

Which of these best defines "waterproof"?

Does not let water pass through it, like a plastic raincoat.

Give one property that makes metal good for saucepans.

Metal conducts heat well, so heat from the cooker spreads quickly through the pan. It is also strong and hard.

Is a wooden spoon hard or soft? How could you test it?

Hard — you cannot dent it with a fingernail or bend it easily.
Key takeaways
  • Waterproof or Not?: testing which materials let water through and which keep it out.
  • Some materials let water or light through, others block them: A sponge soaks up water while a plastic bag keeps it out — one is absorbent and the other is waterproof.
  • material: What something is made from, such as wood, metal, plastic, glass, fabric or rock.
  • Watch out for: assuming shiny means waterproof
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