I use what is called mule tape, it is 0.5 inch flat webbing reated at 1800lbs even if a knot cuts that to half then it is still 900lb breaking strength. I usually use a bowline to tie off to the tree with the mule tape double reapped around the tree. Also the flat tape will not slip like a rope does.
cheers

This related to a classic problem in rigging for cranes.

In theory 'para-cord', 550, certainly has enough tensile strength if it was just a question of suspending a single person's weight hanging from two lines. Even given a loss of around 15% for the line being wet and another loss of 25% or so for wear and tear.

But before you go diving into your hammock feeling you are safe there is another issue: geometry.

And here you were thinking that you would never need geometry. LOL.

Lets for a second assume your hammock was instead a stiff board. And lets assume the points of attachments were directly above the ends of the board. You sit your round 250 pound rump down on the center of the board. Each vertical line takes half of this. Each is under 125# of pull.

Things get more complicated as the lines move away from vertical.

Rigged 60 degrees from vertical you looking at each line taking 1.15 times half the total weight. 125# * 1.15 = 144#

At 45 degrees the multiplier is 1.414 so 125# * 1.414 = 176#

At 30 degrees, about where most people tend to rig their hammocks, the multiplier is 2.0. Or 125# * 2.0 = 250#

At 5 degrees the each line is looking at 11.47 times half the total weight. 11.47 * 125# = 1433.75#

The 'flatter' the hammock the more stain is put on the lines. Obviously somewhere between 30 degrees and 5 degrees your going to run into a problem. Para-cord is strong stuff but most of 3/4 of a ton is way too much to expect. Even more so that it loses strength when wet, old and slightly worn.

The obvious answer is to double or triple the para-cord to get a significant safety factor for how your rigging you hammock. The tighter you rig the hammock the sturdier the rigging will need to be.

Don't count out using para-cord. It is good stuff. Triple or quadruple the line and you could pretty much tow a car. Even the heaviest rope is made out of very thin threads.

Wouldn’t the best option be to construct the hammock like a standard hammock in constructed? They use regular rope that probably isn’t much unlike 550-pound parachute cord. What they do is take the multiple lines that are woven together to form the net section and join them up and braid them on either end. Combining multiple lines together in a good braid will multiply the strength of the line considerably (quite a bit more than just by the number of lines, if I recall correctly).