Mean temperature increases of 2.8 degrees C have been reported for viscoelastic foam . Gel products tend to maintain a constant skin contact temperature or may decrease the contact temperature. Gel pads have higher heat flux than foam due to the high specific heat of the gel material. However, in Stewart's study the heat transfer decreased after 2 hours indicating that the heat reservoir was filling. This suggests that the temperature may increase during longer periods of unrelieved sitting (>2 hours). Stewart also found that moisture increased 22.8% over a one-hour period. The relative humidity of the skin surface increases considerably because of the nonporous nature of the gel pads.