I spent some time talking to the reps of two companies about canopy
size, shape and porosity regarding pilot weight and decent rates in
emergencey parachutes at the SSA convention two years ago.

I was told the following:

Para-Phernalia is known for using what they term zero porosity canopy
fabrics. Strong uses low porosity fabrics, don't know about a super
non-permeable fabric. I would not doubt Para-Phernalia's figures. I
would not go over the weight spec on a parachute and would actually
like a bit of a weight margin. In general the fabrics used today offer
lower descent rates with smaller canopies than the old military chutes
generally used 20 or 30 years ago.





John O. Graybill wrote:
The inflated diameter came directly from Free Flight Enterprises, Inc.
When questioned about this, their representative indicated that the
latest technology canopy fabric is super non-permeable and therefore
allows the inflated diameter to be what it is without excessive descent
rates. He also, suggested that the 25' to 26' inflated diameter
requirements comes from the days when canopy fabric was much more
permeable than what is used today. He pointed out that the smaller
canopy is what allows the Mini Softie to be as small and as light as it
is. Finally he reminded me that the parachute conforms to the
applicable TSO which includes demonstrating acceptable descent rates.

If there is anyone out there who has first-hand knowledge about the
safety, reliability, and the role diameter plays in descent rates for
this, or any, parachute, please feel encouraged to contribute.