7 min readConcept sheetOften a 5-mark answer each

Napping and sanforizing

Napping raises fibre ends from the surface for a soft, warm, fuzzy cloth. Sanforizing compresses moist cotton lengthwise so that it hardly shrinks when washed.

Napping toolsRotating rollers with fine wire teeth, or teasels

Napped fabricsFlannel, flannelette, blankets, fleece

SanforizingControlled compressive shrinkage

Sanforized standardResidual shrinkage not more than 1%

Napping (raising)

In napping, cloth passes over rollers covered with fine, bent wire teeth (or, for fine wool, dried thistle heads called teasels). The teeth pull up fibre ends, mostly from soft-twist weft yarns, forming a fuzzy layer, the nap, on one or both sides. The nap is then sheared to an even height and brushed. Napping makes cloth soft and warm (the nap traps still air) and hides the weave; it may slightly weaken the cloth and cause pilling or shedding. Examples: flannel, flannelette, brushed cotton, blankets, fleece, suede cloth.

Nap and pile

NapBrushed up from the yarns after weaving, as a finish: flannel, fleece. Lies flatter and can be thin.

PileWoven or tufted in with an extra set of yarns: velvet, terry, corduroy. Upright loops or tufts.

Sanforizing (compressive shrinkage)

Cotton is stretched during weaving and finishing, so it shrinks on its first wash (relaxation shrinkage). **Sanforizing**, developed by Sanford L. Cluett and sold under the trademark **Sanforized**, removes this shrinkage in the factory.

1
A sample is wash-tested to find how much the cloth would shrink.
2
The cloth is moistened with steam or a water spray so the fibres can move.
3★
It is fed onto a thick, elastic rubber belt passing round a heated roller; as the stretched belt surface contracts, it pushes the yarns closer together and shortens the cloth by the measured amount.
4
The cloth is dried and set on a heated felt blanket in its compressed state.
5★
Result: Sanforized cloth has residual shrinkage of not more than 1% in either direction.

★ one-way, controls the pace

Shrinkage test (for your finishes report)

Problem

A 20 cm × 20 cm square is marked on an unshrunk cotton and on a Sanforized cotton. After washing and drying, the unshrunk square measures 18.8 cm (warp) × 19.4 cm (weft) and the Sanforized one 19.9 cm × 20.0 cm. Find the shrinkage.

Working

Shrinkage % = (original − final) ÷ original × 100.
Unshrunk, warp: (20 − 18.8) ÷ 20 × 100 = 1.2 ÷ 20 × 100 = 6.0%.
Unshrunk, weft: (20 − 19.4) ÷ 20 × 100 = 0.6 ÷ 20 × 100 = 3.0%.
Sanforized, warp: (20 − 19.9) ÷ 20 × 100 = 0.1 ÷ 20 × 100 = 0.5%; weft: (20 − 20.0) ÷ 20 × 100 = 0%.
Compare with the 1% Sanforized limit.

Answer

Unshrunk cotton: 6.0% (warp) and 3.0% (weft), too much for a fitted uniform. Sanforized cotton: 0.5% and 0%, within the 1% limit.

In daily life

Buy Sanforized cotton for uniforms, aprons and hospital scrubs so they still fit after repeated hot washing. Avoid napped cotton (flannelette) for cooks and for children's nightwear near flames: its raised fibres catch fire quickly.

Exam angle

2 marks: “What is sanforizing?” A controlled compressive-shrinkage finish that pre-shrinks moist cotton on a rubber belt, so the Sanforized cloth shrinks no more than 1% on washing.

5 marks: “Explain napping and its uses.” Wire-toothed rollers or teasels raise fibre ends from soft-twist weft; shearing and brushing; soft, warm, hides weave; pilling; flannel, blankets, fleece; nap vs pile.

10 marks: “Explain napping and sanforizing finishes.” Napping: method, effects, examples, nap vs pile. Sanforizing: need (relaxation shrinkage), process on rubber belt and felt dryer, 1% standard, uses; shrinkage calculation.

Remember it

Napping = brush it up (soft and warm). Sanforizing = squeeze it short (no shrinking, 1% at most).