??? 4 x 1" filters, each with a surface area of 10 square megamicrons, provide a total of 40 square megamicrons when assembled into a box. A single 1 x 4" fil

??? 4 x 1" filters, each with a surface area of 10 square megamicrons, provide a total of 40 square megamicrons when assembled into a box. A single 1 x 4" filter strapped to a fan gives a total of 10 square megamicrons. How are those the same surface area? Ah! I get it, because of the pleating. I guess it depends on whether the greater incoming airflow interferes with itself once it gets squeezed between pleats.