I used plastic (evergreen) rod - 0,5mm
I roll it under the knife with gently pressing down the knife. Very gently ! If you use to much power - knife cuts down.
I rolled 3-4 times up&down until I reach visual effect of 2-3 or 4 turned concavities. Then I pressed more to cut down.
after deformation (I used metal bars with different diameters to press them on rubber gum) looked quite OK:
polyester is very fragile - to much power when rolling or shaping causing breaks
I hope it helps....
to be honest I spoiled 4cm of plastic bar initially to get first item looking quite OK.
