Designed to underpin the understated elegance of Stella Mc Cartney's clothing, these 'Alter Mat' knee boots are crafted from supple synthetic material with a matte finish. They're defined by a chic square-toe profile and are set on stiletto heels for subtle elevation. Lower-Impact Materials. This product is made using at least 50% lower-impact materials or ingredients. Find out more about our NET SUSTAIN criteria here.