This article has been kindly written by Mark Creasey.
Why do fabrics stretch?
Stretch fabrics (knit fabrics) are made using interlaced looped fibres rather than woven fibres. The ‘knit’ or loops give the fabric some of its stretch, alongside elastic fibres which have stretchy properties themselves; for example lycra/spandex/elastane (three names for the same fibre), rayon/viscose (two names for the same fibre) or polyester.
What is stretch and how is it calculated?
The stretch of fabrics is expressed either as ‘2-way’ or ‘4-way’. 2-way stretch is horizontal, running across the fabric from selvedge to selvedge. 4-way stretch is both horizontal AND vertical, running across the fabric and up/down the fabric.
Stretch is expressed as a percentage and is quite simply calculated –
Stretched fabric width – Original fabric width
——————————————— x 100 = Stretch percentage
Original fabric width
For example: If you have a 10cm square piece of fabric, stretch it across it’s width until you feel resistance. This fabric stretches to 15cm so the horizontal stretch is 50% (15 – 10 = 5, divided by 10 = 0.5, multiplied by 100 = 50%).
Now repeat this process from top to bottom of the fabric. This piece of fabric stretches to 13cm, so the vertical stretch is 30% (13 – 10 = 3, divided by 10 = 0.3, multiplied by 100 = 30%).
So this fabric has 4-way stretch, written as 50%/30%. If there is no vertical stretch then the fabric has 2-way stretch, written as 50%. Simple!
What can I use different stretch fabrics for?
Knit fabrics can vary greatly in stretch, even within a specific category of knit fabric, but in general the following is a good guide:
Type of Fabric
Type of Stretch
2-way or 4-way
Dresses, Skirts, Tops, Pyjamas, Shorts
Dresses, Pencil Skirts, Leggings, Baby Clothes, Tops, Pyjamas
Ponte De Roma
Dresses, Skirts, Jackets, Cardigans
Cardigans, Jumpers, Dresses
Cardigans, Jumpers, Dresses
The type of fabric you use for your project will depend on the requirements of the garment. Your pattern will normally specify which types of fabric you can use and any required stretch. As you get more confident sewing with stretch fabrics you can also use them for patterns designed for woven fabrics. Take a look at the following articles for some great hints and tips for converting patterns from woven to stretch fabric:
For tighter fitting clothes like leggings/sportswear, 4-way stretch is essential as the fabric will need to stretch both ways (e.g. around the legs and up and down the knee joint).
For looser fitting items or for fitted items which don’t need to give, 2-way stretch will usually suffice, but you can still use 4-way stretch fabrics.
The advantage of 4-way stretch is that you can use the stretch/pattern in either direction. 2-way stretch will offer more stability for fitted clothing, similar to a woven fabric, but will also give you some room to breathe!