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Welding cable is usually classified as a type of industrial power cable. It's much more flexible than THHN wire or any type of electrical wire. There are two types of flexible welding that I'll tell you about and a few other types of single conductor rubber cable (http://www.centralplaincable.com/html/en/products/rubbercable/) that are very similar.
Welding is made with 30 awg bare copper strands for added flexibility. It has an EPDM rubber insulation which is also more flexible than PVC insulation. It's fairly well known that it's more flexible than battery cable but welding cable has a extra flexible, heavy duty cable, as well, called Super Vu-Tron.
Super Vu-Tron has 34 awg bare copper strands to make it even more flexible than the standard. Super Vu-Tron also has a much tougher insulation because it's meant for an industrial job site where it might be run over and dragged on concrete or other rough surfaces. It only comes in an orange jacket unless you want to have it specially made in a different color. If you did that it would be about a 15,000-25,000 foot minimum run quantity.
Another similar type of electrical power cable (http://www.centralplaincable.com/html/en/products/powercable/) is known as DLO cable, or Diesel Locomotive. The difference is in the flexibility and thickness in insulation for added protection. DLO cable is much less flexible than welding cable because it's only made with 24 awg strands of tinned copper wire. The 24 awg strands are much bigger than the 30 awg welding cable strands so the DLO cable won't be nearly as flexible. Locomotive cable is actually 2000 volts instead of 600 volts to provide more power to the application. Diesel locomotive cables can run above ground or in conduit and raceway when necessary.
There are still many other types of single conductor cables such as stage lighting cable and Type W. Then you can get into the multi conductor power cables like SOOW cable and multi conductor portable cord products. Those are similar to the extension cords you might have in your home except they're made much more rugged and labeled as an industrial power cable.
Make sure you speak to your wire and cable supplier before buying any products. You might be purchasing more or less than you actually need which could dramatically change the pricing. Copper is very expensive per pound and the insulation types can be expensive depending on the cable. Make sure you get everything you need at the lowest possible price by speaking to a qualified wire and cable sales person.
WesBell Electronics sells all the different single conductor house electrical wiring (http://www.centralplaincable.com/html/en/products/buildingwire/374.html). We will set you up with Welding Cable if you need something for your home welder or the Super Vu-Tron welding cable for an industrial application. If you need something more heavy duty than we can get you a 2000 Volt DLO Cable as well. We will match up any power cable to your specific situation because we have the knowledge to do it.
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