what exactly is parachute fabric?

I understand that Sil-nylon was first used as parachute fabric, but they might not use it today. If you're referring to a "parachute" hammock then It's probably just a nylon or rip-stop nylon.

so if parachute fabric is just another kind of nylon, then what are the differences between them? I mean, there are
parachute nylon
taffeta nylon
oxford nylon
...
does anyone know about their differing properties?

> parachute nylon
This describes the application, not the fabric.

> taffeta nylon
> oxford nylon
Subtle differences in the weaving process, often used to fool the consumer in marketing literature. The terms can be misapplied too.

A genuine plain weave is usually finer than a taffeta, which is often (as far as I can tell) done with an air-jet loom. A plain weave is often slightly dearer. Oxford usually applies to heavier fabrics.

Cheers

I have a military parachute that I am making a huge tipi out of,and it appears to be ripstop nylon