Allbirds shoes are designed without logos, labels or special detailing. They’re constructed from ZQ-certified merino wool (meaning sheep are raised sustainably and humanely according to strict standards). The wool is specially knitted into a superfine weave — each fiber is about 20 percent the width of a human hair — so it’s not scratchy.
Washable insoles also are formed from merino wool fabric, and soles are green polyurethane made from castor bean oil. The idea is to create something not only sustainable but breathable, durable, comfortable and all-purpose.
Water was used as blowing agent. The rate of forming was increased by increasing catalyst and water content. On other hand the cell size of the PU decreased with increasing amount of the catalyst and water content.