Authentic Acoustic Flexible Core | Martin Guitar By: Martin Guitar September 2, 2021 A video overview of Martin's easy-to-play and rich-sounding strings. Read More Tags: Martin Guitar, Strings Authentic Acoustic Flexible Core | Martin Guitar By: Martin Guitar September 2, 2021 A video overview of Martin's easy-to-play and rich-sounding strings. Read More → Tags: Martin Guitar, Strings