Exhaust gas treatment device and method for making the same

A method of making a device for treating exhaust gases, comprising:

• providing a mounting mat comprising melt-formed glass fibers containing silica, wherein the melt-formed glass fibers are formed by
• treating the melt-formed glass fibers whereby the treated glass fibers have a silica content greater than the silica content of the glass fibers prior to being treated and whereby the treated glass fibers contain at least 67 percent by weight silica;
• heat treating the leached glass fibers prior to formation of the mounting mat, or heat treating the mounting mat, prior to wrapping the fragile structure;
• wrapping the mounting mat around a fragile structure adapted for treating exhaust gases;
• and
• disposing the fragile structure and the mounting mat within a housing, whereby the mounting mat holds the fragile structure resiliently within the housing, and wherein the mounting mat exerts a minimum holding pressure for holding said fragile structure within said housing of one of (i) at least about 10 kPa after 1000 cycles of testing at a hot face temperature of about 900° C., a gap bulk density of from about 0.3 to about 0.5 g/cm3, and a percent gap expansion of about 5 percent, or (ii) at least about 50 kPa after 1000 cycles of testing at a hot face temperature of about 300° C., a gap bulk density of from about 0.3 to about 0.5 g/cm3, and a percent gap expansion of about 2 percent.