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How to care for synthetic yarns

This is the final article in our series of looking into different fibre types, how they behave and how to care for them so that your handmade items keep looking as good as the day you finished making them!

What are synthetic fibres?

There are many different types of synthetic fibres and they are used in various applications which range from the carbon fibre bodies of racing cars to yacht sails. Even the parachute of the NASA Perseverance Mars Rover which touched down on the Red Planet not too long ago used synthetic fibres made by Heathcoat Fabrics of Tiverton, in Devon here in the U.K. no less!

But let’s head back down to Earth and the world of crochet and hand knitting to discuss the fibre types we might come across in our making endeavours.

The geek’s definition is: “a manufactured fibre produced from a polymer built up from chemical elements or compounds”. In layman’s terms it is a fibre that has been manufactured as opposed to one that occurs naturally.

History of synthetic fibres

The first synthetic fibres were an attempt to make artificial silk in the late 1800’s. Rayon - also known as viscose - was developed using fibres made from mulberry bark. It was originally produced in France before the British company Samuel Courtauld & Co took it over to the USA and by 1910 scaled manufacturing up, because it was up to 50% cheaper than silk.

In 1931, Wallace Carothers discovered nylon while working at DuPont. This was the first truly synthetic fibre made completely from petrochemicals. “Nylons” became popular in the late 1930’s as an alternative to silk stockings and was then used for parachutes and other military applications in place of silk.

After World War II the floodgates opened with the rights to the earlier invention of polyester by Whinfield and Dickson at ICI in England being bought up by DuPont in 1946. In the 1950’s acrylic became popular as a more cost effective and mothproof alternative to wool. Since then, many other man-made fibres have been invented for special end uses such as Kevlar for stab proof vests or Nomex flame retardant fibre to name but two.

How are synthetic fibres produced?

Man-made fibres are usually formed by forcing a solution through holes in a spinneret which looks somewhat like a shower head into air or water to form a continuous thread. The shape and size of the holes in the spinneret can be changed to give a different handle or aesthetic effect to the fibre, making the surface more shiny or dull for instance. This thread is then either used as a continuous length i.e. nylon used in sock yarn, or in the case of acrylic yarns it can be cut into staple fibres to give properties more akin to wool.

ACRYLIC is probably the most popular fibre used in hand knitting and crochet worldwide. It was first developed by DuPont as an alternative to wool in the 1940’s but mass production didn’t get going until the 1950’s. It is made by extrusion and the filaments are then texturised – adding an artificial crimp into them - and then cut into staple fibre before being spun in a similar way to wool. Acrylic isn’t as elastic or absorbent as wool but is warm, lightweight and soft as well as being inexpensive. It is also a suitable alternative if you find wool a bit itchy or have sensitive skin.

It won’t be the end of the world if it accidentally gets chucked in the washing machine on a hot wash, because it is hard to shrink. What might happen, however, is that the colour may bleed. Having said that, it does like a little bit of gentle heat to relax and soften the fibres but must NEVER have a hot iron placed directly on its surface as it will melt! Also, blocking won’t change the shape of an item like it can with wool, but it is useful to help relax the fabric and align the stitches. It has a good stitch definition so is good for showing up textures. It is great to use for baby and children’s items as it can withstand frequent washing.

NYLON is generally used in its continuous filament form, incorporated into a blend with wool for knitting and crochet yarns. It is often added into sock yarns to give them extra strength and help make them a bit more durable, especially around the heels and toes where most wear will occur.

Regenerated cellulose fibres including VISCOSE & RAYON were the first man-made fibres to be produced using cellulose fibre from bark or wood pulp and then dissolving it and extruding it. Their use has fallen out of fashion, because the manufacturing process is quite environmentally unfriendly.  

In recent years a new process has been developed using sustainably sourced eucalyptus fibres as well as renewable energy and reusable solvents. This fibre is known as LYOCELL or TENCEL. It was developed and scaled up for manufacture by what was by now called Courtaulds Fibres, the same company that had first scaled up the manufacture of “artificial silk” nearly a century earlier!

Lyocell is very cotton-like in its handle and is cool to the touch. There are also now alternatives being developed using bamboo instead of eucalyptus as the raw material from which the cellulose is extracted. But not all of these yarns have the same traceability of their manufacturing process as lyocell does. It is always a good idea to buy yarn from reputable brands with a firm ethical stance and strong environmental credentials.

Metallic Fibres

Metals such as gold and silver have been used in very thin threads to decorate fabric for centuries. But because they were extremely expensive, they were reserved for use in fabrics for kings and nobles. Nowadays the metallic, sparkly fibres used in yarns for knitting and crochet such as LUREX or STELLINA are actually nylon or polyester fibres with a thin, metallic coatings applied.

They can be added as a filament and plied with the yarn or cut into staple fibres and mixed into the fibre blend before being spun into a yarn. The staple fibres can feel a bit itchy if you have particularly sensitive skin. The filaments often give a more subtle sparkle but without the itchiness.

How to wash and block synthetic yarn items

Firstly, it is really important to get your gauge right, because it is harder to change the size and shape of the finished garment through blocking as it would with natural fibres. Your gauge swatch can also be useful later on before blocking and finishing your item. More on that next:

Man-made fibres are generally easier to care for than wool: They don’t have scales on the fibre surface to get felted and tangled up. They are sometimes prone to pilling however. Therefore, it is best to treat your garment gently if you are unsure. As always, look at the instructions on the ball band and use these as a guide. If the yarn is, for instance, a wool/acrylic blend then treat it as wool but be careful if applying hot steam as you may “kill” the acrylic part. It does sound a bit scary, doesn’t it?

Let us explain: If the acrylic is heated up past a certain point, the fibres will start to melt. Applying this deliberately as a technique, you can manipulate the fabric to the shape you want it to be, and the stitches will then set in place for good. This can be a desirable effect and give the finished piece a better drape, BUT IT IS IRREVERSABLE!

You may wish to practice on a test swatch. Remember? The one that you made earlier to check your gauge to see if ‘killing’ it will give you the effect you desire. Please make sure to never touch the surface of your work directly with a hot iron, because you will end up with a ruined item and a melted sticky mess on the iron hotplate!

Many synthetic yarns will be machine washable and may also benefit from a tumble dry on a low heat to relax them. If you are going to machine wash, it is always advisable to put the item into a mesh laundry bag or even a pillowcase to give it a bit of protection and stop it snagging on other items in the wash. Also, use a delicate or wool cycle at no more than 40oC using a detergent designed for delicate items. A couple of pumps of a gentle liquid detergent like Knit IQ Delicate Wash can be added to the dosing drawer of the machine to give a bit of extra nourishment to the fibres.

Generally, it is better to spray- or carefully steam block items made from synthetic yarns. There is no real advantage to be had from wet blocking. Here’s how to do it:

Firstly, pin out to the correct measurements onto a suitable surface. KnitIQ Blocking Mats make this easy for you with grid lines in both inches and centimetres. Make sure to use rust proof pins. Again, KnitIQ Blocking Pins are ideal for this. Then simply spray or gently steam your item and leave to dry naturally.

We have really enjoyed writing this series of articles! Thank you for reading and please let us know if there are any other fibre-related topics you would like to know more about. We’d be delighted to help. And finally, as always, please continue to share your makes with us on social media. We’d love to see what’s blocking on your mats this Spring!