Q: Is the water repellent backpack a waterproof backpack?
A: The water-repellent backpack is not a waterproof backpack. Although there is only one word difference between the two, the waterproof performance of the two is completely different. If you want to understand the difference between the two, you must first figure out what the concepts of water repellency and waterproofing refer to.
Whether it is a water-repellent backpack or a waterproof backpack, its function depends on the performance of the fabric. The backpack itself does not have these effects, because the fabric has the corresponding characteristics, so the finished backpack will have the corresponding function.
Water-repellent fabric refers to the deposition of hydrophobic compounds on the surface of the fiber, leaving pores on the surface of the fabric, air and water vapor can also pass through, generally water droplets (like lotus leaf water droplets) will be formed on the surface of the fabric, and there will be no penetration and diffusion. And wet the inside of the backpack to achieve the water-repellent function like a lotus leaf. However, water repellency is not really waterproof, but to reduce the absorption of water by the fabric, so that the water can be "pulled away" on the surface of the fabric, and the water will seep into it after a long time.
Water-repellent processing uses various chemical materials to attach a layer of ultra-fine "needle beds" on the surface of the fabric, so that the tension on the surface of the fabric is less than the cohesive force of the water, so the water droplets will form water droplets and roll away instead of spreading out and soaking. If this layer of needle bed structure is flattened or covered with oil stains, the water repellency of the fabric will be greatly reduced, or even begin to absorb water. The water repellent effect of the fabric will gradually weaken or even fail with washing and long-term use.
The waterproof fabric refers to coating a layer of grease, paraffin, rubber or various thermoplastic resins on the surface of the fabric to fill the pores on the surface of the fabric to achieve the purpose of waterproofing, but at the same time the fabric is not breathable. The current waterproof treatment often uses a waterproof film to prevent the penetration of water molecules, but the film itself is too fragile, so it is necessary to rely on the cooperation of the surface cloth, the film, and the inside to achieve the waterproof function. Waterproof fabrics are classified into different grades due to their different waterproof capabilities. From IPX1 to IPX8, the higher the grade, the better the waterproofing time and effect. Fabrics with high waterproofing grades can be used in diving, and the waterproof effect is particularly good.
For example, when there is a sudden rain outside, if there is a light rain, if you are walking in the rain with a water-repellent backpack, the rainwater will not penetrate into the backpack in a short time, and the water droplets can slide down from the backpack in the shape of lotus leaves. However, if it takes a long time, the inside of the backpack may also be soaked by rainwater, and the degree of wetness is related to the amount of water droplets and the residence time. The waterproof backpack is different. Even if it is exposed to the rain for a long time, the waterproof backpack will still be blocked by the rainwater and protect the contents of the bag from getting wet.
