The most common and most likely answer to this crossword clue is the 8 letter word ARMBANDS
I've seen this crossword clue in The Guardian
A
R
M
B
A
N
D
S
More clues leading to the result ARMBANDS
Buddy explains!

The straight part
We know that "they’re blown up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they’re blown up = armbands.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 ARMBANDS mean?
ARMBANDS noun- A band worn around the arm, usually to symbolize protest or mourning.
- A band worn around the arm of the captain of a team.
- An inflatable band worn round the arms to keep afloat in water