The most common and most likely answer to this crossword clue is the 8 letter word INFLATED
I
N
F
L
A
T
E
D
More clues leading to the result INFLATED
Buddy explains!

The straight part
We know that "filled with air" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case filled with air = inflated.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 INFLATED mean?
INFLATED verb- To enlarge an object by pushing air (or a gas) into it; to raise or expand abnormally
- To enlarge by filling with air (or a gas).
- To swell; to puff up.
- To decompress (data) that was previously deflated.
- Filled with air or fluid
- Expanded; in a state of inflation, of abnormally increased size, amount, etc.
- : In a state of higher cost.
- Pompous; arrogant (of a person or ego)
- Containing excessive, meaningless words, particularly for show
- Higher that the true figure