Adsorption, not absorption.

Absorption is a sponge soaking up water — molecules move into the body of the material. Adsorption, with a "d", is something else: molecules bind to the surface, held by weak chemical attraction.

A single 75 g pouch of activated bamboo charcoal contains roughly 1,300 m² of internal surface area per gram — about half a basketball court of microscopic landing pads, folded into the material. Odour molecules, formaldehyde, ambient humidity all bind to those surfaces and stay bound.

A few hours of direct sun once a month resets the pouch. Heat breaks the bonds, releases what was held, the material is ready to adsorb again. Two years of quiet work. Ten minutes of sun. Repeat.