The laces on my hiking boots broke years ago, and instead of going out of my way to buy a replacement pair, I replaced them with some lengths of paracord I had kicking around, albeit with the intent of eventually getting proper laces. I never got around to it, and the bright yellow and pink cords are still working great, giving no indication they're ever going to wear out. Now whenever I tie up my boots, I wonder what is it about boot laces or shoe laces that makes them so much more preferred than your average cord?
Aglets, shoelaces being easy to find and in the right lengths, the smooth exterior and if you have the right kind, the ease of tying and staying in their knots.
As a hobby knot tyer, (and member of the International Guild of Knot Tyers) I use mountain boot laces to try out the knots I am working with, rather than paracord.
On the other hand, I know enough people who make their own laces out of cord of the right size and with a smooth enough surface for the shoes they are used in.
Reasons to make their own:
Longer lasting laces.
Needing non standard lengths.
Needing non standard diameter laces.
Needing two different lengths due to having an insole or two very different feet.
Wanting a colour or design which is not available in their (local) shops.
As long as the ends are finished in a way that works, they are happy with their laces, often so happy that they never go back to shop bought ones.
While I do agree with using other readily available string and might do it one time, I do not think braiding your own is useful. See my answer here on Arts and Crafts Stack Exchange.
One 'knot' that is very useful for making (temporary) shoe laces out of other string is the whipping to finish the ends. Here the Common Whipping on the animated knots site (others are available.)
(The site I linked to in the first word of this answer is that of Ian Fieggen, who has a great site about shoe laces, their knots and whatever else you may need to know about them.)
I have tried paracord, and don't like it. True paracord is kernmantle construction, with a braided sheath and linear core. The sheath wears too fast. The hard braided nylon cord works well. You may want to buy a variety of sizes. 1/8 is hard on hands. 3/16 is too fat for some eyelets. 5/32 is my preferred cord. You can sometimes get cords in really interesting colours which make it easy to find your boots in a pile by the door.
You can buy aglets at some fabric/sewing notion stores. Crimp them on with pliers. Other ways to keep the end from fraying.
- Wrap the cord tightly with duct tape before cutting it. (This works well for larger ropes too.
- Melt the cord instead of cutting it. This often results in a hard blob that won't pass through eyelets. Squeeze flat before it hardens.
- Dip the end of the cord in varnish. (This works better if you thin the varnish first.) Depending on the surface treatment of the cord you may need to use an oil base varnish. (Some repel water.)
- Ditto using paint.
- Dip the end in the basin of a candle. (Wears quickly)
The main distinguishing attribute of shoelaces is that they are manufactured to be of a specific length that is intended to be compatible with standard shoes. Changing the length of rope-like object (i.e. paracord, shoelaces, string, yarn, etc.) tends to be difficult without either spending a significant amount of effort securing the new end (whipping, aglets, etc.), or degrading the structural integrity.
There are also material differences; paracord is designed with tension being the primary concern, while shoelaces have more varied stresses. And paracord tends to have a circular cross section, while shoelaces come in both circular and flat.