In my case, it depends! Sometimes, using cardboard is much better and more sustainable than using some recycled plastics. Furthermore, if you look for maintaining certain sustainability, plastics shouldnt be your first option... In addition, when you make something that you need to wash, then I wouldnt go for any support material, neither plastics nor cardboard, and I play with shapes, gauge and wise filling...
Thats how I do it, but I asume everyone has their own tricks!
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