soundproofing foam is designed to absord sound to limit reflections making the sound in the room you are recording in better. it's very thick. i would not recomend using it as a wind screen at all as it probably would degrade the audio quality prior to reaching your mic caps.
windscreens are a different design and foam. much more porous(sp?) so as it won't degrade the sound quality while it diffuses the wind coming through.