How much bigger should you make a resist to account for shrinkage?

We know that the amount of shrinkage in wet felting depends on many variables. Among the most important are:

• The wool type: breed, microns, fiber length. Fine wool shrinks more than coarser wool.
• The number of wool layers: if they’re odd or even, how many you lay. Also, thin layers shrink more than thick ones.
• The layout method: chevron will shrink more than the traditional layout, for example.
• Decoration: if you add silk, viscose, fabric, or pre-felts.
• Fulling methods: which ones you use, how many times, in which direction, was it evenly fulled, was it fully fulled. Aggressive fulling methods cause more shrinkage than less aggressive ones, as well as more fiber migration.
• Even the water temperature and the way the wool is dyed can influence the way it shrinks.

So, the only way to know what your results will be is to make samples before beginning a project, unless you always work with the same wool type, so you get to know very well how it behaves.

After you’ve made your sample, you need to calculate your shrinkage rate. There’s much confusion around this, mainly because sometimes people mention percentages and others shrinkage rates.

If you feel confused too, don’t worry. It’s not because you’re not good at math.

There’s actually a very simple way to make this clear. To make things easy, I’m going to ask you to forget about percentages for this next step. Just think about shrinkage rates. Keep this in mind, and I guarantee you’ll never have a problem with this again.

MAKING A SAMPLE

Cut a piece of paper measuring 30cm x 30cm. If you work with inches, you can make it 12in x 12in. I recommend you stick to always making it 30cm x 30cm or 12in x 12in. This will be the template for all your future samples.

Place this under the bubble wrap, so it doesn’t get wet. If necessary, tape it to the table to prevent it from moving.

1. Layout your wool and any decorations you need to add.
2. Use the same type of wool and number of layers you intend to use in your project.
3. Felt the sample using the fulling methods you prefer to work with.
4. Full it completely.

NOW LET'S LOOK AT THE SHRINKAGE RATE

Measure the final size of your sample both horizontally and vertically. Let’s say the piece measures 16.5cm x 16.5cm.

The next step is to divide the initial size by the final size.

Initial size / Final size = 30 / 16.5 = 1.8

In this case, your shrinkage rate would be 1.8

WHAT NOW?

Let’s say you now want to make a table runner that measures 40cm x 100cm (final size).

You now need to multiply both measures by 1.8:

40 x 1.8 = 72

100 x 1.8 = 180

That means you need to make your layout 72cm x 180cm. If you were to make a pattern for your table runner, this is exactly how big it would need to be.

But, of course, you’ll need to use the same wool type, the same layer thickness and everything else you’ve done with the sample.

And this is the way you know that, after felting, you’ll get a final size of 40cm x 100cm, just like you intended.

FREQUENT QUESTIONS

Now, let’s address a couple of frequent questions felt makers have about their samples. 

WHAT IF I STARTED WITH A SQUARE, BUT MY FINAL SAMPLE TURNED OUT TO BE A RECTANGLE?

There are 2 reasons why your sample has a different length and width after shrinkage, even though you started out with a square:

You have an odd number of layers:

If you laid 3 layers, your felt will shrink more in one direction.

This isn’t a problem. In fact, that’s what you should expect. But you have to take that into account when working with an odd number of layers.

You have an even number of layers:

If your felt shrank more in one direction and you have an even number of layers, that means you fulled more in that direction. In this case, you can always full a little bit more afterwards to make your sample even.

You need to watch for this during the fulling process. Keep a measuring tape or a pattern with the final size at hand to control your fulling.

Remember that, when something is handmade, you might not always do exactly the same thing for all sides. We’re not machines. For example, we can make a bit more pressure on the felt sometimes.

But that can be easily corrected if you control the size of your felt during the fulling.

MY FINAL SAMPLE ISN’T SQUARE, SO HOW DO I CALCULATE THE SHRINKAGE RATE?

• If the difference is small, for example one side measures 16 cm and the other 17 cm, you can use the average 16.5 cm
• If the difference is big and you have an odd number of layers, calculate 2 shrinkage rates: one horizontal and one vertical. And work with these two in your project.
• If the difference is big and you have an even number of layers, something went wrong. So, you should either full more where it’s necessary or just redo the sample.