“The Sound of Silence” – how do you achieve it? Hacker Industries, Inc.’s products are integral in achieving improvements in sound and fire attenuation with its full line of FIRM-FILL® Sound Control Mats (SCM) and FIRM-FILL® Gypsum Concrete Underlayments (GCU). With over three billion square feet installed nationwide, FIRM-FILL® SCM and GCU are the acoustical and underlayment solutions for new construction, renovation and repair projects.