Unbreakable Extra Heavy Duty Round Boot Laces Shoelaces 33" Guaranteed for Life. Virtually Unbreakable Iron lace Bootlaces are made with 100% Advanced Para-Aramid Fibers that are 20 Times more durable than Kevlar bootlaces Stretch-Free, Non-Slip shoelaces that lace up tight and stay tied. Color won't fade. Stronger than Steel - Amazing 1500 lb. breaking strength in a 1/8" (3mm) diameter means these will fit any boot and will never break when pulled tight. The World's longest lasting boot lace. Highly Abrasion, Wear, Chemical, UV and Corrosion Resistant Fire Proof - Our shoe laces are heat and fireproof to 630 F (332 C). Made for firefighting, welding or anyone who works hard and expects their equipment to last.