Porosity: Glider health check!

by Brett Janaway


Paraglider Porosity Check

Paraglider porosity is the measurement of the amount of time it takes for a certain volume of air to pass through the paraglider canopy fabric. To test the porosity of a glider, we use a local test house who has a JDC MK 1 Porosimeter, which is the most used porosimeter in the paragliding industry. The MK 1 measures the time necessary for 0.25 liters of air under 4hPa pressure to go through 38.5 cm2 of cloth.


This is the table that we use to interpret the results:

  Canopy Condition     Time (Seconds)  
New >284
Excellent 283-111
Good 111-55
Satisfactory 54-37
Well Used 36-19
Fail <19

So how does porosity affect your glider?

New gliders are tested by various agencies/organizations to determine their performance and safety. When these agencies test gliders, the gliders are new from the factory and have very little porosity. Because the structure of paragliders is formed by pressurization, the porosity of a glider also relates to its pressurization. The behavior of a glider will change as the porosity increases. This change in behavior might be, among other things, glide ratio, speed, resistance to collapses, recovery from collapses, handling in turns, and surging. In addition to the performance being affected, the durability is affected as well. If a glider is more porous, it means the material has degraded and it is weaker than it was when you first bought it. If the material is weaker, it can tear easier. These tears might occur when you are launching or landing near rocks or sticks. However, if the material of your glider is significantly weaker, it may even tear during an event while flying, such as a large frontal collapse. Tearing of a glider from a collapse is very unlikely, but it has happened before.


How do you take care of your glider to slow down the again process?

The most popular source of the aging of a glider is UV exposure. You should always keep your glider out of UV when possible. If you are on launch or in the LZ and your glider is unpacked, cover it up with something to prevent UV exposure. If you fly in places where UV is strong, such as Australia, or towards the equator, your glider will age faster than it would in places where there is less sunshine, or less UV.


Is water bad for my glider?

Water is bad for your glider if it is stored in a damp state. The continued exposure to moisture will weaken the canopy, and the lines. If you get your glider wet, its important to let it dry out as quickly as possible. No need to frantically dry it out, but don't let your glider sit overnight, packed up without letting it dry out first. However, we recommend letting the glider air out at room temperature, out if direct sunlight. Exposing a wet glider to direct sunlight can affect the materials (such as lines and stitching). Lines can shrink and weaken when wet and exposed to direct sunlight. If your glider has somehow ended up in saltwater, we recommend hosing it off with some fresh water to get the salt particles off the glider and let it dry in the shade, or inside.


What about abrasion?

Abrasive materials, such as sand and dirt can degrade the protective coating on the canopy. A common protective coating is a layer of silicone on the inside of the canopy material. So, if you fly in places where you're ending up with sand in your glider, you should do your best to remove these materials from your canopy so they don't continue to wear on your canopy. We've seen some grasshoppers in places that actually take bites out of the canopy material to get themselves out.


Where should I avoid storing my glider?

To increase the lifespan of your glider, store it in a dry cool place. Keeping a glider in the trunk of your car in the heat can weaken the protective coating, or affect the lines.


December 2013