As she was suffering from congestion every morning, I had to check on the internet soon after we get back home from where I identified some, and in the following day I bought one pack. After opening the package, I realized that these fabrics are not made of any type of plastic, which turned me septic about their ability of preventing moisture entrance, and keeping away allergenics.
In the very first day of using one of this cover, my niece awoke one hour late and came to the living room much relaxed than the previous days. I was very worried at the beginning, thinking she had difficulty sleeping when she went to bed, but she told me that she had slept at same time than previous days except the fact that she did not suffer from congestion in that particular morning.
I thought that the cover was still very new to spread something allergenic. So, it was safe to me not to give credit to the recommendation of using that pillow covers. But from this day forward my niece continued forgetting to complain about the anomalies she had previously experienced and I kept myself quite just to not recall for her of the suffering.
Twelve months have gone now. Even after washing and drying them for several times, their membranes and quality zippers continue protecting my niece from mildew, allergens and bacteria. In addition, my niece has commented that the fabrics permits the heat and air to pass across. However, they have remarkable ability of avoiding moisture such as saliva and sweat to flow.
These fabrics would also be very useful for people living in a place where the rooms can have some parasites or insects.