When sourcing selvage denim, you must prioritize fabric weight (measured in oz/yd²), typically ranging from 12oz to 21oz for premium garments. Ensure the fabric is woven on vintage shuttle looms, which creates the characteristic 'self-edge' (selvage ID) that prevents unraveling. You should also verify the dyeing method, specifically looking for rope-dyed indigo, which ensures better color depth and unique fading characteristics over time. Additionally, check the shrinkage rate; 'Sanforized' denim is pre-shrunk to less than 1-3%, whereas 'Unsanforized' (shrink-to-fit) can shrink up to 10%.