I need Kevlar laces as my boots get exposed to metalic sparks and other heavy punnishment, for welders, fire fighters, many heavy industries, Kevlar laces are almost an essential, (they don't melt or burn easy and are extremely strong) and I pull hard when lacing, I have NEVER broken a Kevlar lace unless it was very old and trashed--eroded 80% thru in places and that won't happen quickly.  The ends are the only flaw due to weak plastic wrap that will sometimes fail after a while, this allows ends to fray but doesn't ruin lace. (A dab of silicon sealer or some other liquid 'rubber' worked into a frayed end and squished tight together will do for a fix) Kevlar is tough and you could probably hang your car engine from one of these laces new--incredibly strong stuff.  Leather laces don't melt but are way too weak to consider, nylon are strong enough but melt and wear too easily and for me they last only a couple months at best, then I'm tying knots in them to get thru the day.  Kevlar last for a yr or two minimum no matter how badly I punish them.  Easily worth the price if less then $15 per pair, $12 is common.  Even if you don't abuse boots and laces the way I do, IF YOU EXPECT YOUR BOOTS TO LAST MANY YEARS YOU SHOULD CONSIDER LACES THAT WILL ALSO LAST THAT LONG, and these might.  ((I also pay extra for my custom boots to be stiched with Kevlar thread--well worth the extra $20 for boots that should last 10 yrs rotated with one or two other pair of boots, and cost some $500/pair.))

(((A tangent:  I have 2 or 3 pair of expensive, custom fit, top quality work boots in use at anytime (Westco's), and I send each in for a re-sole or rebuild once.  I also oil at least a couple times per yr., a couple Shoe Goo sessions for life of boot, etc.  I estimated I pay about $200/year for heavy work boots that fit and function as well as possible--probably about the same cost as if I bought cheap boots with minimal protection, bad fit and needing to shop boots 3 times per year.)))