Well you probably want to know what the weight of the fabric is. To do that measure how much you have (or cut 1sqft) and weigh it.
Second you would probably like to know what material it is. The two most common 'types' are taffetas and ripstops. Ripstops are easily identified by the 'grid' they make. Taffettas are tightly woven. There is a difference in thread count but it's hard to actually know without counting....
Hold it up to the light and it will 'tell' you how many threads.
The second part of the second part is what it is made of. The two that are pretty similar in feel are polyster and nylon. Most people use nylon for hammocks. Although some use an inner layer of polyester because it's a bit softer to touch. Anyway the best way to tell is by doing a burn or chemical test
. The formic test is much clearer IMO.
The last thing you'd like to know is if it's coated. Is it uncoated, dwr coated, or waterproof? It's going to be pretty dull on both sides if it's uncoated. It also has a slightly different feel. If it's got one shiny side that might be dwr. The best way to test is to see if the fabric holds water like mentioned above. If it does hold water it's either silicone impregnated or polyurethane coated (PU). The PU coat looks ummm....coated on while the impregnated looks more 'in' the fabric.
Clear as mud?