Bill, I've made impromptu hammocks from bed sheets and blankets and some ski rope, so just about any fabric will work.
Uncoated ripstop or taffeta works fine. Walmart in these parts has a $2/yard rack and I've found all my hammock fabrics there. (back when it was $1/yard. ) grin
Make sure it's uncoated. Coated won't breath.
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paul, texas KD5IVP