Question about shrinking for you techies and scientists
 

What makes cotton shrink:
a. water
b. Hot water
c. hot air when drying
d. other

I just did a bunch of yardage I got at Goodwill, and I did the loads differently. The firsts one I did I washed it then dried it on hot in the dryer. I usually fold the fabric an extra time lengthwise and serge the cut ends to prevent all that fraying and the thread nests. The ones I dried came out all wonky and are going to have to have the ends either cut off or unsewn, and then the yardage will need to be pressed.

The second load I washed and then hung to dry. I don't think I will be able to tell if they have shrunk more or less than the ones I dried.

Anyone ever done any experimentation on this???

Well, I haven't experimented, and am not a scientist, :p but imho (from experience) water alone doesn't cause cotton to shrink, but hot water does, as does heat from a dryer.

Cotton shrinks because of the tension that is applied to it during the construction of the fabric. The tension is released by heat from the washer, dryer, steam and even sunlight, which causes the fabric to be reduced to its natural size.

I've had fabric shrink just from spraying it with starch.

I have measured (lengthwise and crosswise) hundreds of pieces of Fabric before and after washing them, almost all of them shrink. Usually in only one direction or another . I do not know ahead of time which way it will shrink.

The time it would take to experiment would just take away from my sewing.

I just pre-wash everything before I use it. I use coldwater Tide and dry on regular heat or low heat. If it shrinks I don't know about it.

I was curious enough to see if it was worth my effort.

I became aware of shrinkage when I was going to sell some cat print fabric that only measured 35 inches long - and when I watched the piece being cut - it was 37 inches long.

I prewash and dry all my fabric before I use it. No surprises later when I wash it. I have used spray starch, Best Press or Magic Sizing when I iron and the moisture and heat from the iron has shrunk the fabric.

Cut a 3" square of fabric before washing and compare to the finished product.
There are so many reasons why some cotton shrinks and why some cotton does not. Always good to be safe.

I found my refrigerator, stove & make my cotton clothes shrink! LOL