1. General: For a quick overview of filter fabrics/geotextiles see this Wikipedia page. Not really anything here about the function of filter fabrics in roof construction, but it does give you an idea of what they are.
2. Safety: See this Material Safety Data Sheet for health and safety information about filter fabric at the Henry Company website. This is only an example and other products and brands may be different.
6. Manufacturers: See here for filter fabric/geotextile manufacturers.