Synthetic fabrics are man made fibres, usually from the meta or para aramid families but do also include carbon fibres.
They are regarded as high performance, hard wearing fabrics but do come at quite a high cost. They have generally gained their fame as used by fire brigades and in the motor racing industry. They are also used by the military and security forces.
Unlike treated fabrics, that protect by actually burning and producing an oxygen scavanger, synthetic fabrics just don't burn at all until the oxygen concentration reaches about 30%. Synthetic fabrics also swell up when exposed to heat as well as flame and are usually treated with flurocarbons to encourage liquids to run off them. This makes them a better choice if steam or hot water is an issue.
There main disadvantage is that molten metal sticks to aramid fibres so they cannot be used in welding processes or foundaries.