The secret of GORE-TEX fabrics lies within its revolutionary bi-component membrane. The expanded PTFE portion of the membrane contains over 9 billion microscopic pores per square inch. These pores are approximately 20,000 times smaller than a drop of water, but 700 times bigger than a molecule of moisture vapor. So whilst water droplets cannot penetrate the GORE-TEX membrane, moisture vapor (a gas) can easily escape. Integrated into the ePTFE structure is an oleophobic, or oil hating substance that allows moisture vapor to pass through, but creates a physical barrier to contaminating substances such as oils, cosmetics, insect repellents and food substances. The result is a durably waterproof, windproof and breathable membrane.