How do I add custom sizes or attributes and map them to variants?

Go to Settings → Preferences → Custom Attributes and create fields like Fit or Fabric Weight.

In Settings → Preferences → Variants, map any attribute to a Shopify variant (e.g. link Fit to Size).

Type new values (e.g. “3XL”) directly in the grid, or select them from a dropdown depending on your attribute settings.

Use the attribute tokens (@fit, @fabric_weight) in your title/description templates.