For sack-cloth or netting i personally, would do this;
take a dish-cloth ( i dont know if they are called something different in other countries), a cloth you wash dishes with anyway. In the UK they are white and have a shabby blue or red seam.
Cut it to the size you want then soak it (immerse it) in PVA glue.
Leave it to dry a bit, then mould it to the shape you want. Different cloth's have different weaves, so just find one that looks most like the effect you want.
I did this for shabby robes for my Ogres, but i am sure it would work for netting/ nets.
Here's a pic to help visualize the finished thing (it drys rock hard, so is pretty sturdy when dry);



I hope this helps a bit mate.
*just re-read your question. When the cloth is soacked in PVA glue pull it/ stretch it out so the weave parts out more creating more gaps that you can see through. I did the opposite for the cloak things above, because i wanted a more clothy look, but i am sure if you pull the cloth, spread the weave and let it dry it would work. If it doesn't you have only lost the price of a dish-cloth and the time it takes for it to be soaked in PVA!

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