Stretch factor for an elastic means how much that elastic can stretch.
Sewing patterns that use elastics must specify the stretch amount for them. Also, if the pattern uses different types of elastics, for each type of elastics, the pattern instruction must specify the stretch amount.
Elastics have a length and a width. Elastics stretch in lenght direction. Stretch amount is measured on elastic’s length only. Width of elastics varies: thin elastics are used for panties. Wider elastics are used for bras. Even wider – for waist bands etc. For lingerie elastics, usually if the width of the elastic grows, the stretch amount decreases – but this is not a rule!
How to determine the stretch factor (percentage) for our elastic?
Take a segment of 20 cm long of our elastic – do not stretch. The end of the segment is marked by our thumbs.
The hand with the thumb pointing at 0 (zero) will remain still
Stretch the elastic pulling only the right hand
Stretch as much as the elastic allows, do not pull to rip it!
Note the value where our right thumb is pointing
Look for your value in the table bellow and see what your elastic stretch factor is.
How much your elastic has stretched:
The elastic stretch factor is:
Bellow are 2 examples on different elastics. I want to determine stretch factor for each one. Click on pictures to enlarge.
The blue line shows where 20 cm are. But the right red arrow shows that the elastic stretch to 28 cm. From the table above we see that this elastic has a 40% stretch factor.
The blue line shows where 20 cm are. But the right red arrow shows that the elastic stretch to 36.5-37 cm. From the table above we see that this elastic has a 80-85% stretch factor.
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