As mentioned in the previous blog posts, when determining the amount of positive ease for a woven fabric, consideration must be given to the subjective perception of wearer comfort, design detail and garment type. Whereas when determining the amount of negative ease for knits, the amount of ease will vary depending on design considerations, garment type, fabric fiber content, fabric weight and fabric construction(type of knit). For example, a lightweight knit with a high fiber content, such as cotton or rayon, will have more stretch than a heavyweight knit with a low fiber content, like wool. Or, a knit made with a yarn containing a spandex / elastane /lycra core will have a higher stretch ratio than a knit without a yarn containing spandex / elastane /lycra. As a result, a pattern drafted for a cotton knit with a negative ease of 2% will not fit a spandex knit that has more stretch and requires a pattern drafted for 12% negative ease. Or, a pattern designed for high performance athletics will have a different degree of ease than a garment designed for fashion.
There are exponentially more variables that must be considered when determining the amount of negative ease to be incorporated into a pattern made for knits versus positive ease to be added to a pattern made for wovens. For example, when working with a woven, if a pattern has 3" of positive ease added to the bust circumference and wearer comfort is satisfactory, that same pattern can be used across multiple different woven fabrics. However, if 12% negative ease when used with one knit fabric is comfortable for the wearer, that same 12% negative ease may result in a poor and uncomfortable fit when applied to another knit fabric. In summary, negative ease must always be re-calculated and slopers/patterns must be re-drafted when switching between different knits fabrics due to the variances in stretch ratios as a result of fabric fiber content, fabric weight and fabric construction(type of knit).