They're both "hybrid chemistry" cells. The NCR18650B is an INC cell, lithium-nickel-cobalt. I don't know the specific chemistry for the UR18650Y. Hybrid chemistries, such as INR/NCR/NMC/INC/LCA/etc. are safer than ICR but not quite as safe as IMR.
Here is the NCR18650B datasheet :
http://na.industrial.panasonic.com/sites/default/pidsa/files/ncr18650b.pdf
IMR = highest thermal runaway threshold temperature, lowest temperature during runaway, rarely sparks/flames.
Hybrid Chemistries = lower thermal runaway threshold temperature, higher temperature during runaway, may be sparks/flames.
ICR = lowest thermal runaway threshold temperature, highest temperature during runaway, violent reaction usually with sparks/flames, essentially the same chemistry as LiPo.
But the UR18650Y maxes out at under 4A and the NCR18650B maxes at at 6.4A. They can only be used for
vaping at the lowest power levels. I advise against using them in a Kbox.