Let's match the fibres with their applications:
- Polypropylene (P) is often used in geotextiles, making option 4 the correct choice for P.
- Kevlar (Q) is a high-strength fibre used in bulletproof jackets, so it matches option 3.
- Nylon 6, 6 (R) is commonly used for applications requiring high strength and durability, such as in mountaineering ropes, so R matches with option 1.
- Nomex (S) is a heat-resistant fibre used in firefighter suits, so it matches with option 2.
Thus, the correct matching is P-4, Q-3, R-1, S-2.
Final Answer:
\[
\boxed{\text{P-4, Q-3, R-1, S-2}}.
\]