My wife will be redoing our cushions with our sailrite machine an new open cell foam. We are looking at using material composed of cotton (75%) and polyester fabric (25%) from a fabric store upholstery bolts where there are many to chose from. Then we will scotch gaurd and make them water resistant. We want breathability so we do not get mildew. The cloth is much cheaper when bought this way and there are many more patterns and styles to choose from. It is also more compfortble to sleep on the sumbrella.
The hard part is also cutting the foam to make the odd shappped cushions.