Secret sleepers kind at first in providing material (8)
I believe the answer is:
moleskin
'material' is the definition.
(I know that moleskin is a type of material)
'secret sleepers kind at first in' is the wordplay.
'secret sleepers' becomes 'moles' (I can't explain this - if you can you should give a lot more credence to this answer).
'at first' indicates taking the first letters.
The initial letter of 'kind' is 'k'.
'moles'+'k'+'in'='MOLESKIN'
'providing' acts as a link.
Can you help me to learn more?
(Other definitions for moleskin that I've seen before include "Type of fur" , "Furry cotton fabric" , "Thick piled cotton cloth" , "Fur resembling velvet" , "Strong cotton fabric with soft nap, used for work clothes" .)