What is 40 Kilotex in polyester fiber terms?

1 ktex (k = kilo = 1000 as in kg = 1000gms) or 1 000 tex is 1kg/1000meters of fibre.

Example; a length of fibre weighs 1 kg and measures 1000 meters (1 kilometer) long.

This would be 1 ktex of fibre.

40 kilotex of polyester fibre would be a 1000 meter length of polyester fibre which weighs 40 kilograms.

OR

40 kilotex of polyester fibre would be a 25 meter length of polyester fibre which weighs 1 kilogram.