My pennies worth again based on a sailing/sailmaking background... nylon/polyester materials
stretch, Film based materials
shrink ... not a happy combination in a sail ...Nuff said.
however there is some debate about how close to its design loads the material in a kite is working and I suspect the mix of materials can be far more of a fashion/look/appeal choice then a finite element based decision....
I personally like the Mylar in my 2~4 as I think it adds to the look and lets face it that kite probably does see some loads... but I would like to see one made out of a hybrid cloth like some of the Code Zero materials that are becoming the norm for grand prize downwind sails (a very light weight laminate) ... also finding favour in Radio Controlled model yachts! .... Likewise my Speed series kites ..... anything that is about keeping loaded and 'flying' I think is OK to play with laminates....
1, 1.5 and 2's where precision and stable accurate hovers are the game .. don't want it .. prefer something forgiving and stable (flying shape wise) .....
There really is a strong sailing analogy ... Yacht sails are mostly laminates for heavily loaded, narrow angles, upwind sails (think speed series/powerblast needing good shape to fly 'upwind' fast) whereas downwind sails (spinnakers/asymmetric's) are mostly Polyester/Nylon... easy to control/less twitchy/nice rounded stable shapes ... Rev 1/1.5/2 etc ...
Oh and I promise I won't mention sailing again....well until the next time anyway