Glossary term
Hydrostatic head
Also known as: Water column
A laboratory measure of how much water pressure a waterproof fabric can hold back before leaking through, expressed in millimetres of water column.
Definition
Hydrostatic head (mmH₂O) is measured by standing a column of water on a fabric sample and increasing the pressure until water penetrates the fabric.
Performance waterproof fabrics typically range from 5,000mm (light rain resistance) to 30,000mm+ (extreme conditions). The critical performance question is whether the seams match the fabric.
Why it matters to DSEAMS
DSEAMS bonded seams preserve the underlying fabric's hydrostatic head across every seam — removing the gap between fabric spec and finished-garment performance.
Related terms
- Waterproof-breathableA fabric construction that blocks liquid water from entering while allowing water vapour to pass through — enabling sweat to escape from a sealed garment.
- Barrier membraneThe thin functional layer inside a laminate that blocks liquid water while allowing vapour to pass.
- Laminate constructionA textile assembled from two or more layers bonded together — typically a face fabric, a membrane and a lining or backer.