Glass is generally warmer than window paper. This is due to the higher thermal conductivity of glass compared to window paper. Glass has a thermal conductivity of about 0.8 W/m·K, while window paper, which is typically made of thin plastic or foil, has a much lower thermal conductivity, around 0.03 W/m·K. This means that glass can transfer heat more efficiently than window paper, making it warmer when in contact with a heat source. Additionally, glass is a better insulator than window paper, which means it retains heat better. According to a study by the National Renewable Energy Laboratory (NREL), glass has a higher heat retention capacity than window paper, contributing to its warmer temperature.