Ah, Litz wire. I have 2 spools i got at a surplus  warehouse around 1978. I had to climb up to the second level of pallet storage and i thought i had gold, something like 9/38 or some such, which is totally ordinary, unimpressive today, when you can buy monster Litz from China. Completely insane number of threads. 

I thought i read that Litz is only advantageous up to around 1400 kHz. Also, which surprised me, that if one or a couple threads broke internal to the coil, no big deal. Fortunately for us though the breaks are always at the solder junctions, whether by chemical action or mechanical accident. 

I still have those 2 spools, actually never used a foot of it, and now with the China product available, the gloat factor is much less. I also do have a couple big cylinders of ferrite, no idea what they were out of. You may think that these were no doubt for LF freqs, but the one test i ran, with a one or 2 turn coil at high HF freq, the dipmeter's pointer was almost pulled out of the machine when it plummeted. 

-Hue Miller