100% waterproof, breathable and windproof.  Lined with a wickable fabric, generous depth.
Sizes:
 
Pony - 4ft3 / 6ft
Cob - 4f.6ft / 6.3ft 
Horse - 4.9ft / 6.9ft 
Xfull - 5ft+ / 7ft (fits up to a 18.2hns Shire cross)