Nylon used primarily for inexpensive covers or applications where draining is required. i.e. undercovers
PVC waterproof and inexpensive but not breathable.
Acrylic canvas waterproof, breathable, attractive finish, long lasting UV performance and fade resistant
See colours on http://www.sunbrella.com
Click, Fabric Showroom / marine exterior / marine
Polycotton canvas waterproof, breathable tough and longlasting.
Weathermax waterproof polyester. It is breathable tough and longlasting, lighter than canvas and has very good stretch performance, helping to keep a tight skin which assists water run off.
For product information and colours see http://www.contender.co.uk/Products/contenderweather.html
Stamoid Reinforced Heavy Cover PVC is a high spec material with outstanding UV properties and which retains a soft and supple finish that other PVCs lose quickly. It has a woven backing which is strong but kind to the boat underneath.