The 424 x Arsenal FC x adidas UltraBoost 21 "Black Scarlet" is taken from a larger collection that brings together the LA-based retailer and the London football club. A monochromatic black finish is executed on the Primeknit upper, made in part with recycled Parley Ocean Plastic and accented with a 424 tongue tag in a contrasting red hue - a nod to the interior architecture of Emirates Stadium. Responsive cushioning arrives via a full-length Boost midsole, painted black and supported by a Continental rubber outsole in a secondary pop of scarlet.