Thorn Protection in Cloth: A Layer Bound for Garments Worn in Thorn Scrub

People who work in thorn scrub — clearing land, herding, harvesting, fencing — are protected, if at all, by ordinary clothing chosen without any stated standard for what a thorn can do. This paper derives such a standard. Thorn contact is stated at three force levels: brushing contact at 15 N, pressing or leaning contact at 45 N, and a stumble load at 170 N. Single-layer puncture resistances are stated for six common constructions, from 5 N for T-shirt jersey to 95 N for 1.2 mm garment leather, and layers are combined by an originated stacking rule in which the strongest layer counts in full and each further layer counts at 70%. With a safety factor of 1.25, pressing contact demands a stack resistance of 56.25 N. No single common trouser fabric meets it: work-trouser twill gives 20 N, 12 oz denim gives 35 N, and even 18 oz canvas alone gives 55 N, just short. The lightest stack that meets the pressing bound is canvas over a jersey liner at 58.5 N; the practical leg stack recommended here, canvas over ordinary trousers, gives 69.0 N at a mass of 0.44 kg and a material cost of USD 6.60 for both full legs, while canvas gaiters over jeans protect the lower leg at 79.5 N, 0.266 kg, and USD 3.92. For hands, a single leather glove at 95 N meets the bound at 0.099 kg. Every added layer costs heat: the two-layer stacks carry 80% of the evaporative capacity of a single twill layer over the covered skin. Common practice fails the pressing bound on both legs and hands — denim jeans reach 35 N against the 56.25 N required, and jersey garden gloves reach 5 N and do not meet even the brushing bound of 18.75 N — while the stumble load defeats any wearable stack: the only computed stack that meets it is three layers of leather at 228 N, 1.815 kg for the legs, and 33% residual evaporative capacity, which is a demonstration of the limit, not a recommendation.