Strong highlights and high contrast between light and dark areas, since satin (a shiny fabric) reflects light sharply rather than diffusing it softly.

Because patent leather is a shiny, light-reflective fabric, and soft, gradual shading is the appropriate technique for matte fabrics that diffuse light; using it for patent leather would fail to capture the sharp, high-contrast reflectivity that is a defining visual characteristic of that specific material.

The sheer quality of the chiffon isn’t being communicated; a sheer fabric should show some visible indication of what’s underneath (body contour or underlayer) and use lighter, more delicate linework than an opaque fabric, so rendering it identically to an opaque fabric fails to convey its actual sheer, translucent quality.

The canvas trench coat should be rendered with fewer, harder-edged folds that hold their shape, reflecting the fabric’s structured heaviness; the chiffon scarf should be rendered with many soft, gathered folds that respond readily to movement and gravity, reflecting its light, fluid quality – the difference in fold rendering directly communicates the different physical weight and behavior of each fabric.

It would incorrectly suggest the wool coat has a shiny, light-reflective surface quality, when wool is actually a matte fabric that diffuses light and should be rendered with softer, more gradual shading; the mismatched rendering technique would misrepresent the fabric’s actual visual and tactile qualities to anyone viewing the sketch.

Because sheerness is defined by partial transparency – light and visual information pass through the fabric to some degree, so accurately rendering a sheer fabric requires showing this partial visibility of what lies beneath it; opaque fabrics, regardless of their other qualities (shiny, matte, heavy, light), don’t allow this visual pass-through, so there’s nothing “underneath” that needs to be shown for them.

Even a heavy, structured fabric will show some folding or adjustment where the body bends significantly (like at a bent knee), but these folds should still be rendered as fewer and harder-edged compared to how a light, fluid fabric would fold in the same spot – the fabric still needs to respond to the body’s pose, but the character of that response should reflect the fabric’s actual structured heaviness rather than becoming as soft and gathered as a fluid fabric would.

Because accurately rendering how a specific fabric type folds, reflects light, or reveals what’s underneath is part of the broader skill of making a garment sketch convincingly interact with the body’s pose and gesture; a garment sketched with generic, fabric-agnostic rendering (regardless of whether it’s meant to be stiff canvas or fluid silk) would fail to convincingly show the body’s presence in the specific way appropriate to that actual fabric’s real-world behavior.

More fold lines, generally; light, fluid fabrics respond readily to gravity and movement and are rendered with many soft, gathered folds, as opposed to the fewer, harder-edged folds appropriate for heavy, structured fabrics – erring toward more soft folds would better communicate the fabric’s fluid, responsive quality.

It fails to visually differentiate the two genuinely different fabric qualities; canvas (stiff, structured) and unstructured linen (softer, more relaxed) should be rendered with different fold characteristics (fewer/harder-edged versus more/softer) to accurately communicate their different physical properties, so using identical rendering for both misrepresents at least one of the two fabrics.

Because fabric type is a core piece of design information that a sketch needs to communicate accurately, and a single generic rendering style applied to every fabric type would fail to convey these real, meaningfully different material qualities; developing distinct rendering approaches for different fabric behaviors allows an illustrator to accurately communicate the intended fabric choice for any given design, rather than leaving fabric information ambiguous or, worse, actively misleading.

Understanding these techniques allows the designer to sketch out multiple versions of the same silhouette rendered in different fabric qualities (shiny versus matte, heavy versus light) to compare how the same design would actually look and feel in different fabric options, helping inform the final fabric decision based on a more accurate visual sense of each possibility, rather than deciding on fabric without this visual comparison tool.