Coefficient of Increase and a Percentage of Shrinkage ?
Updated: Jan 9
1. Percentage of Shrinkage
Feltmakers often need to know the percentage of shrinkage, they need to know how much their piece is going to shrink. This is called a percentage of shrinkage. We often hear my scarf shrunk 50% or my vessel shrunk 20%.
How to calculate a percentage of shrinkage (PS)?
E.g. scarf layout is 200 cm x 50 cm
The final felted scarf is 130 cm x 25 cm
Let's calculate percentage of shrinkage of a length.
200 cm - 100%
130 cm - X
X = (130 cm x 100%) / 200 cm
X = 65%
This is not a percentage of shrinkage, but what we received after felting.
The Percentage of shrinkage will be 100% - 65% = 35%
We now know that our scarf shrunk by 35%
2. Coefficient of Increase (of a layout)
When making something felted which really needs to fit something or someone, like a cushion, a hat, gloves, a dress or a jacket. How to know the dimensions of the layout to make sure we do not felt a parachute or a mouse hat?
1. I always make a sample using the same materials and the same methods of felting I would use for the main project.
2. Measure layout dimensions.
3. Measure final dry felt.
4. When you know dimensions of the layout and the dry felt. Then, you can determine a coefficient of shrinkage as discussed in my video.
5. The coefficient of shrinkage is a figure, such as 1.5, 1.3, 1.9, 2, etc. This figure can be anything and depends on many factors.
Check this video, an extract from my online class, Felted Textured cushion, on how to calculate a coefficient of increase.