A method for producing a filter pack, comprising: a step of producing an air filter medium based on the following sub-steps: a first sub-step of preparing a sheet including a glass fiber, wherein the content of the glass fiber in the air filter medium is between 30 wt% or more and 99 wt% or less, and having a protruding portion in an undried liquid-containing state, by a method in which: (i) a glass fiber floating in a liquid is processed into paper to obtain a sheet, and a part of the sheet is pressed partially in the thickness direction while being wetted with the liquid, thereby forming a protruding portion; or (ii) a liquid-permeable plate-shaped member itself used to make a glass fiber floating in a liquid into paper has a shape corresponding to a protruding portion, and the liquid-permeable plate-shaped member is used to make the glass fiber into paper; or (iii)a protruding portion is formed with a flat glass filter medium that has no irregularities and a liquid content lower than a predetermined amount being dampened with a liquid; and a subsequent sub-step of reducing a liquid content of the sheet having the protruding portion; and a step of processing the obtained air filter medium into a zigzag shape by alternately repeating mountain folding and valley folding such that the protruding portion holds a space between portions of the air filter medium opposing each other. a step of producing an air filter medium based on the following sub-steps: a first sub-step of preparing a sheet including a glass fiber, wherein the content of the glass fiber in the air filter medium is between 30 wt% or more and 99 wt% or less, and having a protruding portion in an undried liquid-containing state, by a method in which: (i) a glass fiber floating in a liquid is processed into paper to obtain a sheet, and a part of the sheet is pressed partially in the thickness direction while being wetted with the liquid, thereby forming a protruding portion; or (ii) a liquid-permeable plate-shaped member itself used to make a glass fiber floating in a liquid into paper has a shape corresponding to a protruding portion, and the liquid-permeable plate-shaped member is used to make the glass fiber into paper; or (iii)a protruding portion is formed with a flat glass filter medium that has no irregularities and a liquid content lower than a predetermined amount being dampened with a liquid; and a subsequent sub-step of reducing a liquid content of the sheet having the protruding portion; and a first sub-step of preparing a sheet including a glass fiber, wherein the content of the glass fiber in the air filter medium is between 30 wt% or more and 99 wt% or less, and having a protruding portion in an undried liquid-containing state, by a method in which: (i) a glass fiber floating in a liquid is processed into paper to obtain a sheet, and a part of the sheet is pressed partially in the thickness direction while being wetted with the liquid, thereby forming a protruding portion; or (ii) a liquid-permeable plate-shaped member itself used to make a glass fiber floating in a liquid into paper has a shape corresponding to a protruding portion, and the liquid-permeable plate-shaped member is used to make the glass fiber into paper; or (iii)a protruding portion is formed with a flat glass filter medium that has no irregularities and a liquid content lower than a predetermined amount being dampened with a liquid; and (i) a glass fiber floating in a liquid is processed into paper to obtain a sheet, and a part of the sheet is pressed partially in the thickness direction while being wetted with the liquid, thereby forming a protruding portion; or (ii) a liquid-permeable plate-shaped member itself used to make a glass fiber floating in a liquid into paper has a shape corresponding to a protruding portion, and the liquid-permeable plate-shaped member is used to make the glass fiber into paper; or (iii)a protruding portion is formed with a flat glass filter medium that has no irregularities and a liquid content lower than a predetermined amount being dampened with a liquid; and a subsequent sub-step of reducing a liquid content of the sheet having the protruding portion; and a step of processing the obtained air filter medium into a zigzag shape by alternately repeating mountain folding and valley folding such that the protruding portion holds a space between portions of the air filter medium opposing each other.