Acoustic testing of foam-fabric type windscreens done here comes to similar conclusions about the effects of foam/fabric materials on mic reception. Only mostly pure cotton fabric stretched over wire frame proves to be truly transparent at all angles/frequencies due to the 'hollow' of natural fibers containing mostly air. This is not true of all synthetics including reticulated foams that greatly affect sound reception in unpredictable ways.
About 20 years ago Sonic Studios (my company) researched and developed a truly transparent windscreen accessory for the headworn /HRTF baffled omni sets sold here.
More details of this particular windscreen can be viewed at: www.sonicstudios.com/access.htm#whb
The 5-25,000+ cycle flat natural frequency response (uncolored response extending beyond 45,000 cycles) omni capsule reception + acoustically transparent windscreen of a DSM mic is a combination resulting in consistently natural sounding outdoor stereo-surround recordings.
Suggest listening to any of the hundreds of posted recordings using this mic + windscreen system at: www.sonicstudios.com/mp3.htm
Suggestion: You might consider making a custom zeppelin type mic windscreen for yourself using common 92+% cotton jersey fabric (1-3 layers) stretched over homemade wire frame. This would easily outperform anything you can buy today, and save yourself hundreds of dollars over those badly conceived colored sounding commercial zeppelins.