Shipping rates for CustomCat can be set up in the app by using rule-based "by items" rates and setting up the "first item" and "additional item" costs per product group.

CustomCat outlines their product groups (i.e. lightweight, heavyweight, etc.) and shipping prices in the "What’s the cost to ship each item?" section on this page: https://customcat.com/how-it-works/shipping/

By following CustomCat's guide, you can set up multiple product groups in ASR within the CustomCat fulfillment service (i.e. one for lightweight, one for heavyweight, etc.) and each product group can have one or more "by items" rates in it (i.e. Economy, Ground, etc.).

Advanced Shipping Rules has a specific blending rule for CustomCat to handle orders that contain items that belong to multiple product groups.

CustomCat explains their blending rule logic in the "How are shipping charges calculated if my customer orders multiple items?" section on this page: https://customcat.com/how-it-works/shipping/

When an order contains products from more than one category, the rate for the “First Product” will be the most expensive category & the rate/s for the “Additional Products” will be whatever the rate is for each “Additional Product”.

This special logic can be added in Advanced Shipping Rules as a blending rule. When setting up the blending rule, simply select your CustomCat product groups and CustomCat's logic will be automatically applied.