“Sponge mushrooms”  are dried fungal fruiting bodies from various tropical bracket fungi. Once dried, they form lightweight, porous, honeycomb‑like structures that resemble natural sponges. They’re collected from fallen wood in tropical forests, cleaned, and dried for use as décor and microhabitat features.
 
They’re popular because they look organic, last a long time, and offer a texture that contrasts beautifully with wood, leaf litter, and seed pods.