Why do you use a knit for your pillows and not a woven percale?

There are several reasons for this, most significantly is the large volume of water, energy and chemicals required to grow and process cotton woven fabrics compared to the low-inputs necessary for making a jersey knit.  Additionally, the jersey knit is super soft, breathable, cool and more form-fitting on a pillow.  In summary, it's simply a more scrumptious and sustainable fabric.