I don't know if this is the right forum to ask this but this seemed most related.
So is there a breathable (allows moisture escape but doesn't allow water, CO2 or air to pass through) fabric-film available to use as greenhouse cover?
Humidity is huge problem for greenhouses, especially in Hot climates, which are cooled by evaporative cooling. If a breathable material with high transparency is available, it will solve the humidity problem due to high partial pressure of vapor inside than outside.
Tyvac is breathable, but has just 6-8% light transmittance and won't withstand direct sunlight for very long. Also, moisture permeability should be very high (about 500 ml/ hour x square meter) and I don't think even Tyvac can handle that.