The most common and most likely answer to this crossword clue is the 11 letter word FLANNELETTE
I've seen this crossword clue in The Daily Telegraph
F
L
A
N
N
E
L
E
T
T
E
More clues leading to the result FLANNELETTE
Buddy explains!

The straight part
We know that "Cotton fabric" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cotton fabric = flannelette.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FLANNELETTE mean?
FLANNELETTE noun- A type of soft, woven fabric, made to imitate flannel by raising or brushing the fibers in the weft. Frequently used in sleepwear, pillows, and bedding.
- Something made from this fabric.