This is the official 2023–24 third jersey of Athletic Club Bilbao, designed and manufactured by Castore. The shirt features a bold, high-contrast red base with an intricate black abstract wave-line pattern across the entire front and sleeves, creating a dynamic optical effect reminiscent of motion or topographic contours. The crew neck has a black ribbed trim, enhancing structural definition. On the left chest sits the embroidered Athletic Club Bilbao crest — a shield with red-and-white vertical stripes, crossed axes, and the club’s founding year (1898) — signifying heritage and identity. The right hem includes a small Castore brand tag. A prominent 'Kutxabank' sponsor logo is digitally overlaid in the image (not part of the official jersey design), indicating the club’s main sponsor for the season. Made from lightweight, moisture-wicking performance fabric, it offers breathability and stretch for on-pitch comfort, while maintaining a modern streetwear aesthetic off-field. Ideal for fans attending matches, casual sporty styling, or as a collector’s piece for La Liga enthusiasts. The jersey blends athletic functionality with avant-garde graphic design, appealing to both football purists and fashion-forward consumers.