Pattern reduction and body pressure targets

Experimental verification in progress. These planning numbers and Clo3D presets have not been bench-checked against worn sheet yet. Treat them as working marks, not shop-verified claims.

Executive summary

Reduction (negative ease) sets how much the sheet must stretch to close on the body. Gauge sets wall thickness. Local body radius turns wall tension into contact pressure. Those three levers are separate from Clo3D’s Stretch slider.

Headline planning mark for soft NR (relaxed modulus at 100% ≈ 0.8 MPa), fashion-band gauge (~0.40 mm mid 0.39 mm), 12% skintight reduction, mid-limb R = 10 cm: about 0.8 kPa contact pressure — light grip, not medical Class II compression.

Related: Simulating natural rubber sheet in Clo3D · Reduction × pressure sensitivity · Body-region pressure sensitivity

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Three levers

Lever	What it changes	Typical source
Reduction r	Circumferential stretch λ = 1/(1−r)	Pattern geometry (craft tables by gauge band)
Gauge t₀	Current thickness t = t₀/λ after stretch	Roll millimetre / Clo3D thickness
Modulus G	Stress at that stretch	Compound (mill); soft NR calibrated here from film MR100 ≈ 0.8 MPa

Contact pressure for a thin stretched cylinder (Laplace):

$$P=\frac{{\sigma }_{\theta }t}{R}=G(\lambda -{\lambda }^{-3})\frac{t_0}{R}$$

Craft practice usually reduces circumferences, not lengths → approximate λ_z ≈ 1. Vertical measurements are rarely reduced in the craft tables this matrix follows.

Same reduction on a smaller radius (wrist vs waist) raises P. Same reduction on a thicker gauge raises P unless r is lowered with gauge (the craft table does that).

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Skintight reductions by gauge band

Horizontal (circumference) reductions used in the planning matrix:

Gauge band (mm)	Mid t₀ (mm)	Skintight r	λ
0.16–0.20	0.18	14%	≈1.163
0.33–0.45	0.39	12%	≈1.136
0.55–0.65	0.60	5%	≈1.053
0.80–1.05	0.925	2%	≈1.020

Fashion band body tailored / body hug / skintight on 0.33–0.45 mm: 5 / 8.5 / 12%. Thinner bands use larger skintight r; thicker bands use much smaller r. The skintight column is not iso-pressure across gauges — r × t₀ peaks on the thin fashion band.

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Modulus calibration (soft NR)

Postvulcanized HA sulphur NR latex film: relaxed modulus at 100% ≈ 0.8 MPa (Blackley / Porter). Neo-Hookean match at λ = 2: G ≈ 0.457 MPa. Prevulcanized films (~0.4–0.5 MPa MR100) scale pressures by roughly ×0.55. Filled / high-styrene compounds raise M300 sharply — same r then feels much tighter.

Calendered commercial sheet is milled dry rubber, not latex-cast film; treat 0.8 kPa as an upper-soft planning mark for soft NR, not a warranty for every roll.

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Pressure matrix (kPa)

Same G = 0.457 MPa. Sites: waist R = 12 cm, arm R = 5 cm, wrist R = 3 cm. Rounded to 0.01 kPa.

Fashion band (0.33–0.45 mm, t₀ = 0.39)

Fit	r	Waist	Arm	Wrist
Body tailored	5%	0.29	0.70	1.16
Body hug	8.5%	0.49	1.17	1.94
Skintight	12%	0.68	1.62	2.70

At mid-limb R = 10 cm, skintight fashion band ≈ 0.81 kPa (headline 0.8 kPa). Wall tension T ≈ 81 N/m; P = T/R.

Dimensional meaning

• Waist (large R): lowest absolute P for a given r.
• Arm: about 2.4× waist P at the same reduction (radius ratio 12/5).
• Wrist: about 4× waist P (12/3) — distal limbs run high Laplace pressure even when “the same % reduction.”

Thicker gauges with lower skintight r bring wrist/waist closer together in kPa; they do not erase the radius effect.

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Clo3D workflow

1. Draft at body measure; apply 2D reduction for the shop gauge band.
2. Assign NR-sheet preset thickness to match gauge (material simulation).
3. Treat ~0.8 kPa as the skintight rest-pose grip target on mid-limb radii — not a Clo3D material slider.
4. For waist / distal limbs / neck, also check feels-like intensity (reduction × sensitivity) — equal P is not equal wear feel.
5. Log roll ID, gauge, reduction %, and worn feel vs the mid-limb mark.

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Caveats

• Planning model, not a logged wear measurement.
• Craft reduction tables informed the source matrix; this page treats those percentages as already-captured inputs.
• Individual body shape, panel layout, and seams break the pure cylinder assumption.

Deep dive: Why fashion-band skintight peaks

Across gauge bands, skintight r falls as t₀ rises. The product r × t₀ (and the Laplace cells that follow) still peaks on the thin fashion band for the soft-G matrix — thicker stock with tiny reduction is not “the same grip” as 12% on 0.39 mm.

Related fit literacy: Sheet gauge, modulus, and reduction.