Now that you know the recipe for how walls go together, this module walks you through how to choose the right ingredients for yours—based on health, durability, climate, and performance. You'll learn about insulation, WRBs, cladding, wallboard, and rainscreens. You'll explore low-toxicity options like mineral wool, cork, wood fiberboard, and smart vapor retarders, and learn how to avoid mold-prone materials like paper drywall, denim insulation, and regular OSB. We'll discuss VOC levels in common materials, and how to select safer products. With detailed, practical tips on navigating product choices, brands, labels, and installation challenges, this lesson empowers you to design walls that are healthy from the inside out.