Scientists of the University of Leeds, England, found out that an improper cover might be reason for that. During their investigations the scientists discovered that the use of wool covers is ideally regulating the body temperature. One characteristic of wool is that it keeps heat and humidity from the body. According to the scientists the wool cover is also ensuring an ideal temperature in bed when the partners sweat differently. For the study, different fillings were tested for various characteristics like humidity regulation and insulation and how the filled covers cooled down from a temperature of 158° F. Furthermore, their condition was tested in an ideal room climate (45 % humidity, temperature of 62° F).
The analysis showed that over a period of eight hours wool has the characteristic to shield 67 % more humidity than eiderdowns and 43 % more than covers filled with polyester. Furthermore, wool was able to deal with twice as much humidity per hour as other fillings. Also, wool achieved best results with regard to the heat balance. Wool was able to keep the ideal body temperature of 95° F longest.