Fabric in knitting is comprised of:
Yarn, which is composed of fiber, spin, yarn construction, and weight.
Gauge, the number of stitches and rows per inch, which is influenced by yarn weight, needle size, and individual knitting styles.
Fiber, which has its own properties (often different within a category of fiber), how it is spun, and how it is knitted.
Stitch Pattern, how the yarn is worked in pattern will also impact gauge and the fabric created.
The designer (or you, if you are designing) makes stitch pattern choices that will create a certain type of fabric which will behave a particular way with the body underneath it. The same yarn can create fabrics that are soft, drapey, loose, tight, highly textured, lacy, ribbed, etc.. They will all behave differently in terms of fit. Different needle sizes, as well as stitch patterns, can achieve that variety from one yarn.
Fabric, it becomes clear, is everything. And it is completely changeable based on the inputs. So if you make a change to an input, it can change the fit because it changes the relationship with the body.
How Does Fabric Impact Fit?
- The stiffer or heavier the fabric, the more room or ease is needed; the softer the fabric, the more likely it can be worn close to the body and still have good fit.
- The more highly textured, the more body the fabric will have, unless it is knit loosely on larger needles. Looser fabric is drapier.
- Any fabric is a combination of the fiber, the stitch pattern, the yarn, and the gauge.
- Stretch is relatively stable stretch in most hand knits. We don’t usually have stretch in the fibers, like added spandex. There are fibers that have more stretch, like Cormo. Wool has more stretch (memory) than plant fibers. Fibers like alpaca, which are more hair-like, have little memory, and create nicely drapey fabrics. Silk will bring more drape, as will tencel or bamboo. Fibers without memory are less likely to hold their shape and will be impacted more by laundering and wear.
What Role Does Yarn Substitution Play?
I believe the full impact on fabric and fit that occurs when we change yarns is unknowable because we usually do not really know enough about the original yarn. Having no means of comparing it to what we achieve with the substituted yarn. We do the best we can, but the same fit may not be possible because of that substitution. Ideally we would have access to the original to make the best possible substitution. Without that, matching fiber and yarn structure is the only way to mimic the fabric and fit.