Suppose you look for affordable blanked with natural fillings - linen, camel's wool and so on.
Reality is that you can get anything from 100% synthetic filler to around 30-50% synthetic (in top models)
Big factories are making such things:
It is thermally bonded polyester fiber with addition of natural fibers.
Note that natural fibers for such thing can be of lowest quality (ones that are usually go to dump) as they do not need to be long and proper as for real filler.
Add to this that any capitalist producer can't resist to replace with time filler to one with 10 or even 0% of natural fibers content.
More profit such way.
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