What can be used as plant fibres?

[SynnthAura]

In the last patch they added 2 plant fibres as a requirement to build a drying frame. What items can be used as plant fibres, or do you have to go through a process to make the specific item "plant fibre"?

[Droj]

milkweed or cotton

place them in a meatsmoker/fireplace once it has burnt down to ashes then rinse in water.

[Yes]

place them in a meatsmoker/fireplace once it has burnt down to ashes then rinse in water.

This applies to milkweed. Ball of cotton can be used after you've cleaned it.
I think it takes only 2 branches in the fireplace to burn milkweeds.