To start with, it’s probably a good idea to define what is meant by natural and synthetic yarns. A natural yarn is one derived from a living organism – and that can be a plant or an animal – while a synthetic yarn is made from fibres that have been created by a chemical process. Examples of natural fibres include cotton, hemp, linen, silk and, of course, wool (which can come from a wide variety of animals); synthetic fibres include nylon, polyester, acrylic and microfibre.

It’s fair to say that a lot of people assume that natural yarns are better than synthetic ones and it’s true that there are a lot of benefits to using a natural fibre. However, man-made fibres also have their merits and shouldn’t be discounted when you’re choosing a yarn.

Woollen yarns are durable, hard wearing and they hold their shape well, making projects easier to block. They are good at keeping you both warm and cool – by trapping tiny pockets of air next to the skin. Garments made from wool stay warm when they’re wet and they can soak up about 20% of their weight in water before the moisture starts to leak through.

However, yarns spun from animal fibres can be costly and some people are sensitive to such yarns when worn next to the skin – especially any that contain lanolin. You may also need to take more care when laundering anything made from wool – many yarns call for hand washing only. On the other hand, cotton and several other natural yarns are more likely to be washable and seldom cause skin irritation. And plant-derived yarns are often the perfect choice for summer garments.

Synthetic yarns are, generally speaking, machine washable and can cost a fraction of the price of a natural yarn. That said, fabrics made from man-made fibres can pill easily after washing and turn a little shiny. Man-made fibres take dye well and so yarns come in a huge range of colours. You’ll also find a great variety of ‘novelty’ yarns in all sorts of different textures made from synthetic materials. 

There are some projects where a natural yarn is the ideal choice – a lacy shawl just cries out for a lightweight silk yarn and you can’t felt anything knitted with a synthetic yarn. The same can also be said of man-made fibres – there’s a reason why most yarns intended for babies’ and children’s clothing are made from washable acrylic! But, generally speaking, you can use either natural or synthetic yarns for most projects, and of course you can opt for yarns that blend the two and enjoy the best of both worlds. If you want to substitute a synthetic yarn in a pattern that uses a natural one (and vice versa), bear in mind all the above before you choose your yarn and make sure you are use the appropriate weight – and don’t forget to check your tension (see Knit & Stitch Creative Issue 1).