Mylar is a material made from polyester resin that offers high moisture and oxygen barrier properties. These bags provide you with the protection that you need to make sure your food doesn't spoil over time. Salts, pastas, sugars, oats, and grains (just to name a few) are all susceptible to decay from light, oxygen, and water. Mylar bags prevent these elements from degrading your food by blocking out the light and reducing the amount of moisture and oxygen that can enter the bag over time.These Mylar bags have a high tensile strength and, at 5.0 mils thick, are puncture resistance. The zip-seal tops are easy to get in and out of for everyday use or can be heat-sealed above the zip line. The 1 gallon size is perfect for sealing small quantities of food.