Flexible face mask having sides that adhere closely to wearer's cheeks

A flexible face mask having sides configured to adhere closely to a wearer's cheeks, the flexible face mask comprising:

• a rectangular mask body having a long side defining a horizontal direction and a short side defining a vertical direction, the mask body including multiple pleated portions folded in two to four stages,
• wherein the pleated portions are formed so that there is no non-overlapping area between the pleated portions, and both sides of the mask body along the vertical direction are bonded so that a predetermined length of a lower end of each of the pleated portions is not bonded, thus forming a non-bonded portion, and the non-bonded portion is defined between bonded portions, so when the mask is worn and the sides of the mask are deformed from a straight shape into a round shape, the non-bonded portion is inserted between and overlapped with the bonded portions, thereby coping with shape deformation of the sides of the mask and enabling the both sides of the mask body to closely adhere to the wearer's cheeks;
• and
• each of the bonded portions bonded to the both sides of the mask body extends in the vertical direction and has a vertical dimension two to three times a vertical dimension of the non-bonded portion.