Porosity Check

WHAT IS POROSITY?

Porosity is the measurement of the amount of time it takes for a certain volume of air to pass through the paraglider canopy fabric. It works with a 100 mm water column pressure (10 mb).

The result is given in seconds needed for 0.25 litre of air to permeate through the cloth of 38.5 cm2 area under 10 mb pressure. It is then recalculated into standard units and 20 mb pressure with the formula: permeability [l/m2/min] = 5400 / time of measurement

After the test is performed, we use an industry-standard formula to derive a “score”.

Following table is used in interpreting the results:

0 – 27 – excellent “as new” cloth condition
27 – 54 – “ Good ” cloth condition
54 – 108 – “ Used “ cloth condition
108 – 270 – “ Well-used “ cloth, paraglider airworthy
270 and above – “ UNUSABLE ” worn-out cloth, safety cannot be guaranteed

We consider a paraglider with a porosity of less than 270 [l/m2/min] Airworthy.

HOW DOES THER POROSITY CHECK WORK?

​The porosity of the cloth is checked using a POROZIT porositymeter ( JDC Calibrated ). This device measures the seconds taken to allow a specific volume of air to be sucked through a specific surface area of the cloth. The more porous the cloth the fewer the seconds. Porosity is measured at 4 points on the upper surface of the canopy, about 10 to 20 cm behind the leading edge. New cloth can score up to 500 seconds or more. The bottom limit, depending on the type of cloth and manufacturer’s specifications, lies somewhere below 20 seconds

​HOW DOES POROSITY AFFECT MY PARAGLIDER?

​A new glider will have very little porosity (assuming it meets all specifications). Because paraglider’s are designed to maintain pressure between the top and bottom surfaces as they fly, the porosity of a glider can greatly affect its pressurisation. The characteristics and behaviour of a paraglider will change as the material becomes more porous and the porosity increases. These changes can affect the performance of the glider – such as glide ratio, speed, recovery from collapses, handling turns, resistance to collapse and surging.

If a glider is more porous, it also means the material has degraded and it is weaker than it was when you first bought it. The weaker the material, the easier it is going to be a tear. Tears can when you are launching or landing near rocks or sticks.

HOW DO I SLOW DOWN POROSITY OF MY GLIDER?

​The most common reason for aging glider material is repeated or extended UV exposure. Its important to always keep your glider out of UV sunlight when possible. Avoid the glider becoming moist or wet for any extended period of time. While any amount of water won’t immediately affect the glider, leaving it packed over night will not do it any favours. Always air you glider at room temperature if it has become damp or wet. Avoid exposing a wet glider to direct sunlight, this can also affect the materials such as the lines and stitching.