Material provided by hacks principally, or a shire, oddly (9)
I believe the answer is:
horsehair
'material' is the definition.
(horsehair is a kind of material)
'hacks principally or a shire oddly' is the wordplay.
'principally' suggests taking the first letters.
'oddly' is an anagram indicator.
The initial letter of 'hacks' is 'h'.
'a'+'shire'='ashire'
'ashire' is an anagram of 'sehair'.
'h'+'or'+'sehair'='HORSEHAIR'
'provided by' acts as a link.
(Other definitions for horsehair that I've seen before include "It's used in furniture for padding" , "From Arab perhaps" , "this may provide us with many strings to our bow" , "substance, stranded" , "Good stuffing" .)