A and D strings have a solid steel core and stainless steel winding. The Direct&Focused A string uses a new, unique material that is currently being patented.
Larsen Strings A/S, Ingolf Nielsens Vej 14A, DK 6400 Sønderborg, Dänemark, larsenstrings@larsenstrings.com, https://www.larsenstrings.com