Rapid lace system DC's Rapid Lace System - DC's proprietary one string Rapid Lace System allows for easy micro adjustment of the boot's fit - both the upper and lower portions. Just pull up, pull back, and you're locked in. Echo Liner Echo Liner is built of lightweight foam and has a front lacing system with reinforced lace locks, so you can get your foot in the liner more quickly and with less fuss. The Echo liner reduces bulk and eliminates heel lift, and the calf area is lined with soft, comfortable padding to help keep your calves from getting tenderized.