KayCore plywood is a veneer core trade named product manufactured by Columbia Forest Products utilizing our PureBond formaldehyde free gluing technology and any of the veneer species available to us at the given mill where it is produced. The core plies selected for placement in the plywood core adjacent to the face and back meet the requirements for grade "K" as set forth in the ANSI/HPVA HP-1-2004 Product Standard for Hardwood and Decorative Plywood. This provides a very smooth surface with only very small imperfections allowed under the thin decorative face. The entire panel is produced to thickness tolerances well within the range of thickness permitted by the above referenced standard.
Poplar, whether you mean Yellow or Tulip Poplar (Liriodendron tulipifera), or Aspen (Populus spp.), which is sometimes called Poplar or Popple, is the common name to one of a number of various species of trees typically harvested and processed into core stock. These species are typically found in mills east of the Mississippi River. Our western facility may also use white fir, pine, spruce, or hemlock as inner plies.
So, to answer your question as succinctly as possible, poplar plywood is plywood made with poplar core. Kaycore plywood is plywood made with any species, including poplar, fir, pine, hemlock, spruce, or others I haven't mentioned, that is produced to a particular standard.
Hope this helps!