: I'm wondering if anyone has ever built a kayak out of poplar wood.

I've used poplar, but only in 1/4 x 1/4 inch trim strips. It's certainly somewhat heavier than cedar, and not as flexible. I used it because I could get some clear grain material and wanted the light color - would have used pine but couldn't find usable material easily. John Monfoe used some on the deck of his boat, but again, I think his use was limited to feature strips. Check out my website for a description of how I used it.