and insect repellant agent as a result the strands of fiber making up the first element 51 are coated with waterproof agent and insect repellant agent at the same time each of the second and third elements 52 and 53 is made from a non woven fabric the second and third elements 52 and 53 are manufactured using a melt blown method as a result each of the second and third elements 52 and 53 has pliability non permeability and insulation characteristics fig9 is a picture of an expanded surface of a second or third element making up the filter as shown in fig8 as shown in fig9 each of the second and third elements 52 and 53 has pores the pores each with a different size are irregularly arranged the size of the pore should be within a given tolerance mean size of the pores in the second and third elements 52 and 53 may be in a range of 5 to 20 u03bcm included the fourth element 54 is made from a non woven fabric the fourth element 54 is manufactured using a needle punch method the thickness of the fourth element 54 is determined by adjusting either the number of.