Our most loved NANDEX ™ fabric (made famous by our 'Best Black Tights' or 'leggings' for our international customers), now available in Royal Navy. STAX. NANDEX ™ is the perfect combination of a buttery smooth, high-performance fabric that can support you through your work out and your everyday, stylish lifestyle. STAX. 7/8 Tights (leggings) are high waisted with a thick waistband to support and synch.