.....For while the tired waves, vainly breaking,
Seem here, no painful inch to gain,
Far back, through creeks and inlets making,
Comes silent, flooding in, the main.
Sudden onset is how it happens.
Stage 1) Dry skin. No leaking. Inner membrane permeable. Outer fabric layer still dry
Stage 2) Dry skin. No leaking. Inner membrane permeable. Outer fabric layer getting soaked.
Stage 3) Dry skin. No leaking. Inner membrane partially coated on outside by layer of water, becoming 'clingy' and losing permeability to sweat vapour. analogous to situation in a tent where the inner sheet is touching the fly sheet. Outer fabric layer completely soaked.
Stage 4) Clammy skin. No leaking but sweat can't leave the building now. Inner membrane completely coated on outside by layer of water, becoming 'clingy' and impermeable to water vapour. Outer fabric layer approaching saturation point.
Stage 5) Wet skin. No leaking but water being drawn from limited number of small ingress points such as sleeves, holes etc by surface tension effects (the capillary action of 'clingy' membrane). Inner membrane now acting effectively as a plastic bag to channel water to the underwear regions. Outer fabric layer now functioning as reservoir for ensuing 'flash flood'.