The most common and most likely answer to this crossword clue is the 7 plus 6 letter word BLANKET STITCH
I've seen this crossword clue in Financial Times
B
L
A
N
K
E
T
S
T
I
T
C
H
More clues leading to the result BLANKET STITCH
Buddy explains!
The straight part
We know that "How material may be reinforced" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case how material may be reinforced = blanket stitch.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 BLANKET STITCH mean?
BLANKET STITCH verb- To sew (something) using a blanket stitch