Base sheet for total heat exchanger element

A base sheet for a total heat exchanger element comprising calcium chloride in a paper base material, characterized in that the paper base material comprises pulp with a freeness of from 200 to 600 ml both inclusive as measured in accordance with JIS P 8121 except that a pulp collection amount is set to 0.3 g/L;

• the paper base material has a bone-dry basis weight of from 17 g/m2 to less than 23 g/m2;
• content of the calcium chloride is from 6 g/m2 to less than 9 g/m2;
• moisture permeability at a temperature of 20° C. and a relative humidity of 65% is 2600 g/m2·24 h or higher;
• the calcium chloride functions as a flame retardant and a desiccant;
• the base sheet is free of an additional flame retardant in addition to the calcium chloride;
• the base sheet is free of an additional desiccant in addition to the calcium chloride;
• the base sheet is free of a temperature control agent;
• flame resistance of the base sheet, measured in accordance with JIS Z 2150, is grade 1 or 2;
• and a rate of moisture absorption (AM) is from 31% to 40% both inclusive, wherein the rate of moisture absorption (AM) is a percentage calculated using the following equation:
• AM={(A−B)/B}×100,
• where A is a mass of a sample under conditions at 20° C. and 65% relative humidity;
• and B is a bone-dry mass of the sample after heating and drying in an oven at 105° C. for 2 hours.