Mosquito-Net Physics Priced per Bite Prevented: The Aperture-Airflow Trade-Off, Insecticide Decay, and a Replacement Interval

SIMULATED, NOT MEASURED. A model of the bed-net mesh trade-off: woven-screen pressure drop and airflow, logistic mosquito passage versus aperture, insecticide decay, hole accumulation and aperture stretching, and airflow-dependent nightly use, integrated over net life to give bites prevented per child sleeper and a price per bite prevented. Optimum aperture 1.2-1.5 mm (nominal 1.4 mm); replacement at 3.1 years when used-night efficacy reaches 0.70; approximately $0.47 per 1,000 bites prevented per child over that life (6,095 bites prevented against 9,052 with no net). Includes compute.py, the model code that produced every number.