Back sheet ---the water resistant outer layer of diapers

Marion O’Brien Donovan, She was one of the most prolific female inventors of her time and she had received 20 patents in total for her inventions. Donovan was inducted into the National Inventors Hall of Fame in 2015. In the past, infant after used cloth diapers, which could easily cause diaper rash. Marion Donovan, a mother, took the plunge and cut a shower curtain into pieces, then used buttons instead of pins to create a waterproof diaper cover. At first the manufacturers were not interested in her invention, but she did not give up and continued to work hard on her invention. Eventually she received funding for her product and began manufacturing and selling it, which soon became a huge hit. Donovan’s invention leak-proof waterproof diapers that changed sanitary products forever.  

The back sheet is the water-resistant outer layer of the diaper. It can prevent liquids from passing through the diaper and leaking into the baby’s clothes or surrounding environment. The main raw material of the back sheet is polyethylene film(PE film) also called permeable micro-porous film and composite bottom film.

The bottom film looks like a plastic film, actually it's a breathable micro-pore film. The micro-pore is the most critical part, because the minimum diameter of a water drop is 20µm, and the diameter of a water vapor molecule is 0.0004µm. The micro-pore diameter is in between those two diameters. In this way, it is breathable and impermeable to water.

Sinbao back sheet PE film is one kind of hydrophobic film. It allows water vapor and air (but not liquids) to pass through, it’s with good air permeability and would keep baby skin dry and comfortable.