In the test, water pressure under the fabric rises at a set rate until drops appear on top, usually counted at the third drop, and the result is given in centimeters of water column or in millibars. It is the main barrier number for SMS medical fabrics, leg cuffs and protective clothing, and it is driven by the pore size of the meltblown layer. Shot, pinholes and surfactant contamination all pull it down.
Hydrohead dropped to 28 centimeters on the last roll, so check the MB beam for shot.
Results at a 10 and a 60 centimeter per minute rise rate do not compare, so the rate belongs on every report.
Also heard as
- hydrostatic head
- HSH
- water column
Related terms
Meltblown
Web of very fine fibers made by blasting molten polymer from a row of tiny die holes with hot, high-speed air.
SMS
Spunbond-meltblown-spunbond: a three-layer composite of strong spunbond outer layers around a meltblown barrier core.
Shot
Small beads or lumps of polymer that failed to form fibers and sit embedded in a meltblown web.
Pinhole
Tiny hole in a barrier fabric or film that lets liquid or particles through.