Good holiday-cooking question — answering as the UphillTech team:
Muffins and cakes rise because of chemical leavening agents and the expansion of hot gasses, they stay risen because the flour and sugar forms a structure which traps the air, then solidifies enough to hold its shape once the expansion has stopped. Cocoa puffs are made in a process called extrusion, where batter is pressurized and shot out in little spurts. On the release of this pressure the little squirt of batter expands and almost crystallizes in the same way as a muffin or cake, in other words puffs are cooked by a different method, but the processes which make them hold their shape is...
Full answer by GdD: https://cooking.stackexchange.com/a/121140 (CC BY-SA 4.0).
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