Foaming
Fizzing
noun, verbal noun
The departure of bubbles is when bubbles leave something, like a mouth. That's why this is foaming.
発泡 is a technical word used for something that's filled with air bubbles or produces foam. It's often used in materials and product names, like 発泡スチロール (styrofoam), 発泡酒 (low-malt beer), or 発泡剤 (foaming agent).
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. Just be careful to note the reading changes: the はつ gets shortened to はっ, and the ほう changes to ぽう.
発泡スチロールはこの袋に入れてもらってもいい？他のゴミとは分別して捨てるんだよね。
Could you put the styrofoam in this plastic bag? We throw away the rest of the garbage separately.