|For a while I've been looking for information about how to adjust a pattern for woven fabric for stretch.
The general advice seems to be to make the pattern in a smaller size, but since all depends on the amount of stretch in the fabric used I didn't feel very comfortable with this.
I really was looking for some kind of formula that would take the amount of stretch in the fabric into account.
When I ran into the same problem whilst making a pattern in PMB 3 I decided to contact their helpdesk (after all they do also make PMB curves that does allow you to make adjustments for stretch). The helpdesk got back to me with the formula I was after and I thought I might be usefull for others. I know the subject has come up lots of times on the messageboards.
Determine the stretch-factor of your fabric
Fold the fabric on the crosswise or lengthwise grain, several inches from the cut edge or selvage. Measure 4" of the fold, then stretch. If it stretches to 5", it has 25% stretch; if it stretches to 6", it has 50% stretch; etc.
This way you'll end up with a horizontal and vertical stretch factor. The vertical one is only used to make things like swimsuits, stirrup-pants,etc.
So you take the horizontal stretch factor and use this formula:
Adjust your base pattern to zero ease in the areas that are close fitting.
Then you scale between 1 and 3 percent > for each 10 percent of stretch. For example lets say the fabric has 30 > percent across stretch. Using 2 you would scale 6 percent. So you need to scale the width of the patternpieces down by 6%.
What makes you choose either 1,2, or 3 scale is how close fitting the garment has to be. For example 3 is used for swimsuits.
I made a pair of pants using this rule (scaling by 2) and they came out great!
I hope this makes sense, it's a lot easier to do then to try and write it down!