Start with needs, not with the material
Do not begin with a favourite material. Begin with the job. Ask: What must this product do?
- Use needs: strength, stiffness, weight, heat, water, safety for food or skin.
- Making needs: can we cut, bend, mould or join it with the tools we have?
- Money needs: price of the material and the cost to shape it.
- Looks and feel: colour, shine, touch.
- Planet needs: where it comes from and what happens at the end.
Each need becomes a criterion (a test that a material must pass). Write each as a short, clear sentence, for example: 'must hold 1 litre of hot water without bending'.
The structured choice: score, weigh, compare
A structured choice is a method that anyone can repeat and check. Use a table.
- List the candidate materials in rows.
- List the criteria in columns.
- Give each cell a score from 0 to 10 (10 = best for that need). For cost, a cheap material gets a high score.
- Give each criterion a weight (importance). A heavier weight means that need matters more.
- Multiply each score by its weight, add up, and divide by the sum of the weights. The highest total wins.
Total = (w₁×s₁ + w₂×s₂ + …) ÷ (w₁ + w₂ + …)
Then check the winner against the must-haves. A material that fails a must-have (for example, 'safe for food') is out, however high its total.
Natural and artificial materials
Natural materials come from plants, animals or the ground, with little change: wood, bamboo, cotton, wool, leather, stone, clay. Artificial (man-made) materials are made by people through chemical or heavy processing: plastics, glass, steel, concrete, synthetic fibres like polyester.
- Natural: often renewable and low in energy to make, but properties vary from piece to piece and some need a lot of land.
- Artificial: properties are exact and repeatable, and we can design them, but they usually need more energy and may be hard to break down.
- Being natural does not mean 'better'. Some natural materials are over-harvested; some artificial ones can be recycled many times.
Eco-design and the whole life of a product
Eco-design means designing a product so that it harms the environment as little as possible during its whole life.
- Raw material: mining, farming or oil. Is it renewable? Recycled?
- Making: energy, water and waste in the factory.
- Transport: distance and weight carried.
- Use: does it use power? how long does it last?
- End of life: can it be repaired, reused, recycled, or does it go to landfill?
Tools that help: a life-cycle assessment (LCA) counts the impacts in each stage (for example, kilograms of CO₂ made); a checklist or eco-score gives quick marks; eco-construction tools compare building materials by energy used, distance and recycled share. Simple rules: use less material, use materials that can be recycled, make it last longer, make it easy to repair and take apart.
Choosing software, processor and interface the same way
The same method works for the control part of a machine. List the needs, then score the options.
- Software: does it do the job? is it free or paid? is it easy to learn? does it run on our computer?
- Processor (the 'brain' chip): speed, memory, number of input and output pins, power use, price.
- Interface (how the machine meets people or other machines): buttons, screen, touch, wireless link. Think about who uses it: a child, a worker with gloves, a driver.
Eco-design applies here too. A chip that uses less power makes a battery last longer, and software that works on old hardware lets people keep their devices longer.
Key formulas and definitions
- Weighted total = (w₁s₁ + w₂s₂ + … ) ÷ (w₁ + w₂ + …)
- Product life: raw material → making → transport → use → end of life
- Natural = from plants, animals, ground. Artificial = made by people.
- Must-haves first, then scores.
Worked examples
1. A bottle needs strength (weight 3) and lightness (weight 1). Steel scores 9 and 3. Plastic scores 4 and 9. Which wins?
Steel: (3×9 + 1×3) ÷ (3+1) = 30 ÷ 4 = 7.5. Plastic: (3×4 + 1×9) ÷ 4 = 21 ÷ 4 = 5.25. Steel wins because strength is weighted more.
2. Same bottle, but now lightness is weighted 3 and strength 1. Who wins now?
Steel: (1×9 + 3×3) ÷ 4 = 18 ÷ 4 = 4.5. Plastic: (1×4 + 3×9) ÷ 4 = 31 ÷ 4 = 7.75. Plastic wins. The weights, not the materials, changed the answer. This is why we must say clearly what matters.
3. A cup made of glass lasts 10 years and a plastic cup lasts 1 year. Making the glass cup costs 3 times more energy. Which is kinder to the planet over its whole life?
Compare per year of use. Say plastic uses 1 unit of energy per cup. Plastic: 1 unit per year. Glass: 3 units ÷ 10 years = 0.3 units per year. Glass is kinder, because it lasts long. Looking at only the making stage would give the wrong answer.
Common mistakes
- Choosing the material first and then finding reasons for it. Start from the needs.
- Looking at one property only. A strong material may be too heavy or too costly.
- Thinking natural always means green. Check the whole life, not only the label.
- Forgetting the end of life. A product that cannot be recycled or repaired becomes waste.