Why didn't my cotton/polyurethane jeans dye? Can I remove the polyurethane, or use another dye?

Name: Susan

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Linda Knutson's
Synthetic Dyes for Natural Fibers

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Message: I have two great pair of jeans that I need to dye, after two attempts with fiber reactive dyes, I realized the 100% cotton feel is actually 98% cotton and 2% polyurethane. Can I remove polyurethane? Can I dye with another type of dye? Please help.

You cannot remove the polyurethane. It is probably woven right into the fabric, intermixed with the cotton. This is normally not a problem at all! Polyurethane is what spandex is made of; spandex is also known as elastane or Lycra. It's usually very easy to dye cotton jeans or other cotton clothes that contain 2% spandex mixed into the fiber, or even up to 20%. The stretch polyurethane does not take the fiber reactive dyes, but it doesn't matter, since it doesn't interfere with the ability of the cotton fibers to react with the fiber reactive dyes. Coloring 98% of the fiber is always sufficient. You usually can't even see the undyed 2% except when the fabric is stretched.

There are fabrics with a polyurethane coating, made to feel like synthetic leather, but, since your jeans feel as though they are 100% cotton, that's not the issue here. A faux leather coating made of polyurethane or another plastic would make your jeans undyeable, and it could not be removed sufficiently to allow good dyeing. However, in that case the fabric would not feel like natural cotton on the surface at all, no matter how high the cotton content of the original weave of the fabric.

What brand of fiber reactive dye did you use? Did you use soda ash or washing soda along with it? Perhaps something went wrong and you accidentally left out the soda ash altogether. This has been known to happen on occasion, and prevents the dye from fixing.

Also, soda ash does not go bad, but fiber reactive dyes certainly do. If you leave a jar of fiber reactive dye in a hot car with the windows rolled up in sunny weather, the dye can lose its ability to react with cotton within a day, though it should last at least a year or two when stored in a tightly sealed container at room temperature. Fiber reactive dye purchased from a hobby store can sometimes (rarely) be so old before you ever buy it, or have been exposed to so much heat, that it's completely nonreactive and needs to be replaced with fresh dye. (I've never known this to happen with dye ordered directly from a good dye supplier.)

Not all types of fiber reactive dyes are alike; some will work at any temperature over 70°F, but others require much higher temperatures. What temperature did you do your dyeing at?

If you did your dyeing in a large bucket or a washing machine, did you add several pounds of salt? When you use a large amount of water, you need to use salt, though salt is not needed for low-water methods such as tie-dyeing. (See the recipes linked to from my page, "How can I dye clothing or fabric in the washing machine?".)

Your dyeing problem could also have been caused by a finish that was applied to the fabric, coating the fiber. Coatings are not mentioned on the fiber contents label. Were your jeans advertised as being stain-resistant or wrinkle-resistant? The coating required to make clothing stain-resistant makes the fabric completely undyeable, because it resists dye just as it does stains. Water-resistant coatings pose the same problem. The coatings used to make fabric wrinkle-resistant are less of a problem, as they allow some dye through, but they still make it difficult and usually rather unsatisfactory to dye. There's always a risk of undeclared fabric finishes, when you dye commercially-made clothing that is not marketed as PFD (Prepared For Dyeing), though it usually works out okay.

If the dyeing failed because of a mistake in how you used the dye or because the dye was old, then it should be possible to fix the problem. If the dyeing failed because of a coating on the fibers, then no type of dye will work. There is no other type of dye that will work any better on your 98% cotton jeans than fiber reactive dye.

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Why didn't my cotton/polyurethane jeans dye? Can I remove the polyurethane, or use another dye?

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