Moisture management is critical when packaging delicate pastries. Engineers have refined the rectangular disposable pastry box to create a microclimate that preserves texture without extra preservatives. Strategic ventilation channels—laser-cut along the side seams—allow excess steam to escape at a controlled rate of 0.8 g/hour, preventing sogginess while retaining just enough humidity to keep sponge cakes supple. Finite-element simulations model airflow patterns, ensuring that a 4 mm diameter perforation every 25 mm provides optimal pressure balance. Tests on custard-filled Danishes show a 38 % reduction in crust softening after six hours at 22 °C. The rectangular geometry itself aids convection: vertical walls channel warm air upward, creating a gentle chimney effect. To counteract dust ingress during delivery, electrostatic filters made from biodegradable non-woven mesh are heat-sealed over each vent. In colder climates, micro-perforated films with phase-change microcapsules release latent heat when temperature drops, protecting against staling. For high-humidity regions, an inner layer of chitosan-coated kraft inhibits mold growth without altering flavor. The box’s flat top also accommodates a thin silica-gel patch disguised as decorative foil, doubling as an oxygen scavenger. Data loggers inserted during pilot runs confirm that core pastry humidity stays within 2 % of the optimal 12 % for up to 48 hours. These innovations allow small bakeries to compete with industrial giants in shelf-life performance, all within a 100 % compostable structure that costs less than three cents per unit.