Experienced hatters use it (4)

I believe the answer is:

felt

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'experienced' is the definition.
(feeling is a kind of experiencing)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for felt that I've seen before include "suitable for a fedora" , "Fabric of matted wool fibres" , "investigated in touching way" , "examined by touch" , "Soft fibrous material usually under carpet" .)

I've seen this clue in The Irish Independent.

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