It is ok to substitue polyester yarn to nylon yarn and artificial silk but with lower cost and better color.

We professionally produce the polyester yarn with lowe price and high quality. The type we're supplying is 

POY: 75D/36F,100D/36F(48F) ,150D/36F(48F), 200D/96F ,300D/96F 

DTY:  100D/36F(48F) ,150D/36F(48F)  , 200D/96F ,250D/72F ,300D/96F 

FDY:  150D/72F(48F) ,170D/72F , 300D/96F ,450D/144F ,600D/192F  

The product detail is belowing:

Polyester Yarn