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.

Each gram of activated bamboo charcoal holds roughly 1,300 m² of internal surface area — about three basketball courts 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 pouches. 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.