 Within 1960s textiles, cotton fibres expand when wet, bond to many coatings, and cotton fabrics are therefore easily made waterproof and rot-proof, but remain relatively heavy and cumbersome, and far from an ideal backpack textile, while nylon fabrics are lightweight, tough, flexible, easily cleaned, but technically very difficult to waterproof other than by adding coatings (with existing coatings such as polyurethane readily peeling or wearing away), and when untreated are always permeable to water (its fibres don't expand to fill the gaps when wet).Therefore, in the 1960s, robustly waterproof fabrics were still largely based on rubberised coatings, duck-cotton and the like, even though these flexed poorly and added weight.In collaboration with a local company (either BM Coatings or Gordon and Fairclough, sources differ), Karrimor developed an elastomer-nylon process in which toughened nylon fabric was waterproofed without significant weight or additional coatings, and without losing its natural flexibility, durability, texture, or other desirable qualities.