Chapter 1: Where Folds Start / Stop — Tension & Compression Maps

Created by Sarah Choi (prompt writer using ChatGPT)

Where Folds Start & Stop — Tension & Compression Maps

Why fold mapping matters

Folds are not random noise: they are the footprint of forces flowing through cloth. A convincing costume sketch shows where tension originates, where compression accumulates, and how gravity and inertia negotiate the space between. For production, accurate fold logic predicts stress points, informs seam reinforcement, and reveals where volume or ease must be added. Think of folds as field lines in a physics diagram: consistent lines make design choices feel engineered, not decorative.

The mechanics in one page

Fabric drapes because gravity pulls and the material resists via weight, stiffness, and friction. Folds begin where a tensile vector is opposed by an obstacle or where extra length has nowhere to go—shoulder ridges, belt tops, elbow crooks, knee backs, seat curves, and hem shelves. Folds end where force dissipates—at open edges, along seams that consume slack, or at contact planes (torso, thigh, floor). Three variables control the “music” of folds: tension direction, compression reservoir, and flow path (gravity, bias, or inertia). Once you decide those, the fold family becomes predictable.

Anchors, shelves, and channels

  • Anchors are fixed points that pull (buttons, belt hooks, straps, grips, hands). They generate tension rays.
  • Shelves are horizontal supports where cloth can accumulate (waistbands, hips, seated thighs, cuffs). They collect compression.
  • Channels are paths the cloth prefers (grainlines, seam lines, piping edges). They steer fold axes. Draw anchors first, then shelves, then channels; let folds grow from that scaffolding.

Fold families and their triggers

This guide focuses on five families you’ll meet constantly: pipe, zigzag, spiral, drop, and inertial. Each is a signature of how tension and compression are distributed.

Pipe folds (columnar)

Trigger: Cloth hanging from a fixed ridge with vertical gravity dominance; excess distributed evenly. Where: Skirt hems, capes, curtains, sleeves held straight down, robes at rest. Map: Parallel vertical troughs with rounded “pipes.” Spacing widens toward the free edge as mass accumulates. Peaks meet anchors with gentle S‑curves. Design cues: Reads as calm, formal, heavy, ceremonial. Bias‑cut reduces pipe regularity; stiff wovens sharpen ridges. Add slight asymmetry to avoid CG‑perfect regularity. Production notes: Pipe density increases with heavier cloth or longer drops; call out hem weight if you want deep, steady pipes on set or in sim.

Zigzag folds (accordion)

Trigger: Compression trapped between two opposing anchors or within a constrained channel. Where: Inner elbow and back knee when bent, waistbands under belts, stacked sleeves at wrist, scarves jammed between armor plates. Map: Repeating V or Z shapes. The hinge (apex) sits near the compression reservoir; arms of the V aim toward the tension sources. Wavelength shortens with tighter compression. Design cues: Implies activity, tightness, or restraint. Great for utilitarian looks or cramped armor‑cloth interfaces. Production notes: Too many tight zigzags on knits look wrong—knits relieve with stretch rather than stacking. In wovens, reinforce apex with bar‑tacks if the fold is persistent.

Spiral folds (helix, bias‑driven)

Trigger: Fabric oriented on bias around a form; torque or gravity causes wrap with rotation. Where: Twisted sleeves, sashes, skirts cut on bias, capes caught in a turn, turbans, wrapped leggings. Map: Diagonal ridges that travel around the cylinder/cone, often advancing with each loop. The helix angle aligns with bias; direction mirrors the twist. Design cues: Elegant, dynamic, dancerly. Works for characters with grace or mystique. Avoid mixing spiral logic with rigid panel reads unless you design a seam that “permits” the twist. Production notes: Bias consumes length—hems will grow; plan for hang stretch or specify stay‑tape along edges to control distortion.

Drop folds (shelves and cascades)

Trigger: Cloth flows over an edge and falls, creating cascades as it reattaches to the form below. Where: Over belts, pocket flaps, peplums, layered skirts, cloaks draped over shoulders then falling. Map: A top shelf with a break line; below it, semi‑regular scallops that elongate with distance from the shelf. Each scallop is a small pipe fed by the shelf’s slack. Design cues: Soft abundance, layered wealth, or romantic volume. In harsh worlds, make the shelf sharper and the cascades fewer. Production notes: Cascades multiply thickness; call out lighter fabrics or cut on partial bias to preserve motion while avoiding bulk.

Inertial folds (motion‑induced)

Trigger: Acceleration changes (start/stop/turn) throw cloth mass opposite the motion vector. Where: Running capes, skirts in spins, sleeves at abrupt stops, long coats at a leap. Map: Folds radiate away from the moving anchor with lagging arcs. On turns, expect a swing fan with a node near the pivot (hip or shoulder) and a trailing flare. On stops, reverse‑curves form S‑shapes as momentum overshoots then settles. Design cues: High energy, cinematic. Align with action lines; exaggerate tail lag for readability. Production notes: Test with sim or ribbon proxies. Specify hem weights to control flutter vs. snap.

Where folds begin and end

Folds begin at stress concentrators (tight corners, pulled buttons, elbow points) or slack reservoirs (excess length above a shelf). They terminate at energy sinks: free edges, stretch zones that absorb, seams that “eat” slack (gathers, pleats), or flat contact planes. In your rendering, avoid letting folds die mid‑panel without reason—either carry them to an exit or fade them as tension dissipates.

Body zones: predictable maps

  • Shoulders/upper torso: Pipes along sleeve head at rest; inertial fans in swings; zigzags where straps compress.
  • Elbows: Zigzags at inner crook; starburst draglines at outer elbow if too tight; spiral cues when sleeve is twisted.
  • Waist/hip: Drop folds from belt shelf; diagonal drape into pocket openings; compression dimples near closures.
  • Seat/crotch: Horizontal compression under seat when sitting; tension rays from fly button; zigzags at back knee and inner thigh during squat.
  • Knees/shins: Pipes on straight stance; zigzags in crouch; spirals on wrapped gaiters or bias leggings.

Grain, seams, and fold steering

Grain dictates default paths: straight grain favors vertical pipes and clean drop folds; bias encourages spirals and soft S‑curves. Seams act as dams or rails: topstitched seams can arrest fold travel, while piping can channel folds into rhythmic repeats. Place seams where you want order; leave broad panels where you want chaos.

Material behavior cheatsheet

  • Light, fluid wovens (silk, rayon): Long, soft pipes; pronounced cascades; delayed inertial lag with graceful tails.
  • Medium cottons/woolens: Balanced behavior; readable zigzags; stable drop folds.
  • Stiff canvas/denim: Fewer, sharper folds; strong shelf breaks; zigzags with crisp apexes.
  • Knits/spandex: Minimal stacking; tension dissolves into stretch; folds are broader and shallow.
  • Leather/laminate: Resists small wavelengths; favors large‑scale bends and seam‑steered breaks.

Lighting the fold story

Highlights live on convex ridges; shadows fill concave troughs. In pipes, band highlights form a rhythm; in zigzags, alternating peaks create a saw‑tooth light pattern; in spirals, highlights travel diagonally. Keep value bands consistent with fold family or your read collapses. Reserve sharp specular accents for tension peaks or laminated edges.

Pose, camera, and readability

At distance, only the direction and frequency of folds read. Aim pipes and spirals to support silhouette; use zigzag clusters to indicate hinges; stage drop folds to frame motion. For keyframes, pair inertial fans with gesture arrows so animation and costume agree on timing. For orthos, include a grayscale “fold map” callout that marks start lines, flow arrows, and sinks.

Designing with fold families

Choose a dominant family per garment:

  • Ceremonial robes → pipes + controlled drops.
  • Rogues and climbers → zigzags at joints + bias spirals in wraps.
  • Dancers and mages → spirals + inertial fans.
  • Military coats → restrained pipes with seam‑steered breaks. Then modulate with secondary families to avoid monotony.

Production translation

Call out where folds must exist (pattern‑driven: pleats, gathers) versus where they are pose‑driven. If you need persistent zigzags at elbows, specify pre‑shaped seams or insert pleats. If you need clean pipes in a windy scene, add hem weight and stiffer weave. For VFX/cloth sim, supply fold maps and hem weights; for practical builds, indicate interfacings or tapes along break lines.

Common pitfalls and fixes

  • Random scribbles → Start with anchors/shelves; pick a fold family and stick to it.
  • Folds dying mid‑panel → Route them to an edge or seam; reduce amplitude as energy dissipates.
  • Incongruent material behavior → Match wavelength to fabric; knits don’t stack like paper.
  • Bias ignored → Add subtle spiral drift on bias pieces; correct hem stretch in callouts.
  • Over‑noisy keyframes → Reduce families to one dominant; use value grouping to keep silhouette legible.

Exercises for mastery

  1. Draw a cape in three states: pipes at rest, spiral in a turn, inertial fan at a stop.
  2. Sketch a sleeve set: relaxed pipes → elbow zigzags → over‑twist spiral. Annotate anchors and sinks.
  3. Design a belt + tunic with drop folds; vary shelf sharpness and record cascade changes.
  4. Translate the same pose in four materials; note wavelength and amplitude differences.

Checklist before you ship a sheet

  • What is the dominant fold family per garment/panel?
  • Where are tension anchors, compression shelves, and exit sinks?
  • Do grain arrows and seam paths align with fold flow?
  • Are wavelengths appropriate to material weight and stiffness?
  • Do folds support gesture and camera distance readability?
  • Are persistent folds pattern‑encoded (pleats, pre‑shape) or pose‑dependent? Is that clear in callouts?

Closing

Fold logic is choreography in cloth. When you choose anchors, assign a dominant family, and steer flow with grain and seams, your drape becomes inevitable—not improvised. Your worlds will feel dressed by physics, and your production partners will see a map they can build, simulate, and shoot.