This is Dupont’s trademark for elasthane, the artificial fibre that is obtained from a resin known as segmented polyurethane.
‘Lycra’ is a registered trademark of the Invista Group that is part of the US-based chemical group. The most commonly used variety of Lycra in stretch jeans is the T-400 type, which is very resistant to chlorine.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary
