also: くうきふくろ
Standard kanji spelling. The reading くうきぶくろ is the most common pronunciation.
Alternate reading くうきふくろ is less common but recognized.
Compound of 空気 (air) and 袋 (bag, sack). The reading くうきぶくろ uses rendaku voicing on ふくろ, while くうきふくろ retains the unvoiced form.