It's not postiche, wich is indeed artificial hair..wooly / decotwister is used in the florist world as a decoration material. You could use gardenpond filter fibers too but then you have to spraypaint them..
Hanging basket liner is a good alternative and very cheap.
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I think you can get the same stuff from a material shop for making pillows or craft. stuff for filter ponds might be a little bit more pricey as it has to be chemical/bleaching free and non-contaminated.