Functional Finishing
Rupture pressure depends on the wall-to-diameter ratio, not the diameter. Capsule size is a feel decision; the wall ratio is the functional one.
— µN
Force to burst one capsule
Rupture is treated as all-or-nothing at the threshold, with the fraction burst rising linearly up to it — real capsule populations have a wall-thickness distribution and rupture progressively across a range of pressures, so partial release begins well below the nominal threshold. Rubs to depletion also assumes each rub finds fresh capsules, which a repeated rub in one place does not, and it ignores the capsules lost to laundering and abrasion between wearings. Phase-change capsules must survive rather than rupture, so for those the useful reading is the pressure ratio staying comfortably below one under garment pressures.
Microcapsule Rupture Force & Payload Release Calculator — free, with the formula and a worked example, at Textile School.