A system for designing a knit footwear upper, comprising: a computing device configured to provide a user interface for customizing or modifying a footwear design for the knit footwear upper using a user interface display (200, 300); libraries (110, 111, 112, 113) comprising: a color library containing a plurality of color values corresponding to colors of a plurality of materials for manufacture of the knit footwear upper; a heather library containing a plurality of heather patterns for creation by a knitting machine; a lasts library containing a plurality of lasts of various shapes and forms; a grading library containing a collection of previously graded uppers, the collection identifying footwear features for grading a base design for use with a range of shoe sizes; a design module of the computing device, configured to process design changes made to the footwear design via the user interface; a structural rules component configured to provide the computing device with data relating to one or more structural rules associated with physical and/or structural integrity required for a footwear upper to be manufactured and a corresponding base footwear design; wherein the one or more structural rules are to place limitations on a user's ability to modify aspects of the footwear design to maintain structural integrity of the respective footwear upper when manufactured for use by a wearer; a structural evaluation module of the computing device configured to process data to determine whether design changes made to the footwear design via the user interface are acceptable, by: extracting information associated with the corresponding base footwear design and comparing that information with data from the structural rules component to determine whether a design change conforms to the one or more respective structural rules and/or physical limitations associated with the base footwear design; a cost estimation module of the computing device configured to process data relating to a cost of manufacturing a footwear upper based on the footwear design; and a time estimation module of the computing device configured to process data relating to an amount of time needed to manufacture a footwear upper based on the footwear design. a computing device configured to provide a user interface for customizing or modifying a footwear design for the knit footwear upper using a user interface display (200, 300); libraries (110, 111, 112, 113) comprising: a color library containing a plurality of color values corresponding to colors of a plurality of materials for manufacture of the knit footwear upper; a heather library containing a plurality of heather patterns for creation by a knitting machine; a lasts library containing a plurality of lasts of various shapes and forms; a grading library containing a collection of previously graded uppers, the collection identifying footwear features for grading a base design for use with a range of shoe sizes; a color library containing a plurality of color values corresponding to colors of a plurality of materials for manufacture of the knit footwear upper; a heather library containing a plurality of heather patterns for creation by a knitting machine; a lasts library containing a plurality of lasts of various shapes and forms; a grading library containing a collection of previously graded uppers, the collection identifying footwear features for grading a base design for use with a range of shoe sizes; a design module of the computing device, configured to process design changes made to the footwear design via the user interface; a structural rules component configured to provide the computing device with data relating to one or more structural rules associated with physical and/or structural integrity required for a footwear upper to be manufactured and a corresponding base footwear design; wherein the one or more structural rules are to place limitations on a user's ability to modify aspects of the footwear design to maintain structural integrity of the respective footwear upper when manufactured for use by a wearer; a structural evaluation module of the computing device configured to process data to determine whether design changes made to the footwear design via the user interface are acceptable, by: extracting information associated with the corresponding base footwear design and comparing that information with data from the structural rules component to determine whether a design change conforms to the one or more respective structural rules and/or physical limitations associated with the base footwear design; a cost estimation module of the computing device configured to process data relating to a cost of manufacturing a footwear upper based on the footwear design; and a time estimation module of the computing device configured to process data relating to an amount of time needed to manufacture a footwear upper based on the footwear design.