Question
What are the differences between natural fibres and synthetic fibres? Give two examples of each and compare their properties.
Solution — Step by Step
Fibres are thread-like strands used to make fabric. They fall into two groups based on where they come from — nature or a factory.
- Natural fibres come from plants or animals
- Synthetic fibres are made by humans using chemicals (usually petroleum-based)
The three big natural fibres you must know for CBSE Class 6–7:
| Fibre | Source |
|---|---|
| Cotton | Seed pods of the cotton plant |
| Wool | Fleece (hair) of sheep or goats |
| Silk | Cocoon of the silkworm |
Cotton and silk appear together in almost every board exam question on this topic.
Synthetic fibres are made in laboratories by joining small chemical units (called monomers) into long chains:
| Fibre | Full Name / Origin |
|---|---|
| Nylon | First fully synthetic fibre, made from coal + air + water |
| Polyester | Made from petroleum; used in “Terylene” and “Dacron” |
| Acrylic | Synthetic wool — used in sweaters and blankets |
For your exam, remember: nylon was the world’s first fully synthetic fibre.
| Property | Natural Fibres | Synthetic Fibres |
|---|---|---|
| Source | Plants / animals | Chemicals (petroleum) |
| Moisture absorption | High — absorbs sweat well | Low — dries quickly |
| Comfort in summer | Very comfortable (cotton breathes) | Less comfortable, traps heat |
| Durability | Less durable, tears more easily | More durable, stronger |
| Cost | Generally costlier (silk especially) | Cheaper to produce |
| Burning behaviour | Burns slowly, smells like burning hair/paper | Melts and burns, smells like plastic |
| Bio-degradability | Biodegradable | Non-biodegradable |
Natural fibres (cotton, wool, silk) are obtained from nature, absorb moisture well, feel comfortable, and are biodegradable. Synthetic fibres (nylon, polyester, acrylic) are chemically manufactured, dry quickly, are stronger and cheaper, but are non-biodegradable and less comfortable in hot weather.
Why This Works
Fibres are long, thin structures — this shape is what makes them spinnable into yarn. Natural fibres already exist in this form in nature (cotton bolls, silkworm cocoons). Synthetic fibres mimic this shape by forcing molten chemicals through tiny holes (called spinnerets), similar to how a spider spins its web.
The properties follow directly from the source. Cotton has tiny air pockets in its structure, which is why it breathes and absorbs sweat — exactly what you want in Indian summers. Synthetic fibres like polyester have a tighter, smoother structure, so moisture sits on the surface instead of being absorbed. That’s why your sports jerseys are polyester — sweat stays on the surface and evaporates fast.
Biodegradability connects to natural origin. Bacteria in soil can break down plant and animal material because they’ve evolved to do so. Synthetic polymers are relatively new — bacteria haven’t had millions of years to learn how to eat them.
Alternative Method — The Burning Test
If you’re ever given a fibre sample and asked to identify it, the burning test is your practical tool:
- Cotton → burns steadily, smells like burning paper, leaves ash
- Wool / Silk → burns slowly, smells like burning hair, self-extinguishes
- Nylon / Polyester → melts and burns, smells like plastic, leaves a hard bead
The burning test is a favourite in CBSE practical exams and MCQs. Remember: natural fibres leave ash; synthetic fibres leave a hard, plastic-like residue (because they melt before they burn).
Common Mistake
Many students write “silk is synthetic because it is shiny and smooth.” Silk is 100% natural — it comes from the silkworm’s cocoon. Its shine comes from the triangular prism-like structure of silk fibre, which reflects light. Synthetic fibres like nylon can also be shiny, but sheen alone does not make something synthetic. Always go back to the source: if it comes from a living organism, it is natural.