solid core VS stranded for inside speaker cabinet

I recently purchased a crossover upgrade DIY from a popular seller GR research for a Klip 504c however the seller sent me in the kit Solid core wire as part of the kit   , I always thought stranded was best and I haven't really seen solid used before inside of a speaker cabinet , I was taught that electrons flow on the outside of a wire not the inside so having many strands is better vs 1 16 awg solid core wire , I thought that this seller maybe just wanted to save a little money by sending this wire out but he insists solid core is better , my gut wants me to finish this project off with stranded not solid core , I want to ask what's better and why,  is it possible solid wire from the cross over to the speaker is better or is stranded better from the cross over to the speaker? 



"what cables do you recommend please?"

I hestate to use the word "recommend" in that I don’t want to imply that I’m the wire guru and my solution is the preferred solution over others. I’ve auditioned many cables over the years, but my knowledge base does not include many listed here, which may, in fact sound better than what I use. That being said, I've been successful using Audioquest cables in most of my projects with predictable results. Rocket 33, 44 & 88 provide good bang for the buck, although they are not inexpensive. These are set up as single bi-wire, so you are actually getting two cables in one making the cost-per-foot lower than a similar full-range cable. The HF section has smaller conductors, and there’s a little more "meat" in the LF section.

You mentioned Rocket 11. I like this cable on a budget. Just a note, though, that it is actually a stranded cable and not solid core. AQ aligns the strains in straight rows next to each other vs twisting them, which AQ feels creates an advantage. Rocket 33 and up are superior sonically. And, give you the opportunity to spend more money. AQ does offer full range solid core in bulk, but not as easy to find.

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Solid core is absolutely fine and many well known cable manufacturers use it. Many use a stranded cable that each strand is insulated which is referred to as Litz and there’s simple stranded which is like the old Monster Cable which my Wilson Audio W/P 6’s were built with. If I was to rewire the internal wiring of a speaker and was going to use solid core I’d probably use a lighter gauge and do a twisted pair as opposed to a larger single conductor. For your center channel speaker and short runs I bet you’ll be just fine with what came with the kit. If you have not tackled the project yet, I definitely recommend Cardas solder as it has a nice flow to it and easy to work with. Wonder Wire used to make a nice solder too. Hopefully the kit came with enough solder to do the job as the Cardas or TRT Wonder solder isn’t cheap if you have to buy a spool. Good luck and take your time.