 Blends of different natural fibres are common too, especially with more expensive fibres such as alpaca, angora and cashmere.Yarn is selected for different textiles based on the characteristics of the yarn fibres, such as warmth (wool), light weight (cotton or rayon), durability (nylon is added to sock yarn, for example), or softness (cashmere, alpaca).Yarn is composed of twisted strands of fiber, which are known as plies when grouped together.