3PCK-MiraCool Navy Blue Terry Hard Hat Liner for suspension, One Size, #919 - BLUE 3 PACK! 3PCK-MiraCool Navy Blue Terry Hard Hat Liner for suspension, One Size, #919 - BLUE At the top is a built-in, water activated MiraCool pad for cooling The sides are soft, 100% cotton terry that cradles your head while wicking away annoying perspiration. Liner attaches easily to hard hat suspension with hook and loop straps.