Best Core Wood for a BBI Tri-Lam?

[pnwarcher]

I am planning a tri-lam build with bamboo backing and ipe belly. The question is: what is the best core wood for such a bow? Maple is a natural choice, or possibly hickory. I've seen those. If I use 1/8" thick backing and belly, then nearly all the stress will be in the bamboo and ipe, which seems to imply I should use the lightest wood possible for the core and not worry too much about its structural properties. Eastern redcedar seems an excellent candidate. What are y'all's favorite "secret sauce" core woods for tri-lam bows?
Bonus: for the sake of discussion, why not use something absurdly lightweight, like paulowina or balsa? This is a terrible idea, right??

[willie]

I have always wondered if the common favorite, maple is on account of it's  diffuse porous structure?

[High-Desert]

I've always wondered the same thing about using an insanely light wood. I always thought Sitka spruce would be a good choice but I've never seen anyone try it.

[willie]

why not use something absurdly lightweight

too light and it may fail in shear

[Badger]

  On English long bow tri lams I usually use cherry with the bamboo ipe, shipping one to England today. The core is about 1/4" thick.

[PatM]

Maple is the go to wood because  it is the one that reliably has all the desirable traits in a core wood.   In particular it glues very well and has great shear strength.

 While it is tempting to say the core is pretty neutral you will see failures indicating this is not true.
cedar
 Glass bowyers have used very light woods like POC, Alaskan Yellow  Cedar and likely Sitka Spruce as well since the first two are said to work.

[Springbuck]

I messed around a lot with this concept early on and used to use a lot of bamboo flooring for both cores and bellies.  I  tried black cherry, Q/S yellow locust heartwood from the trunk (which was very light and porous), white mulberry heartwood, red elm, sycamore, and black walnut, all lightweight woods.

It didn't seem to make much difference what I used. Even when I was reverse-tapering the cores so there was more light wood at the tips.  None of them blew unless there was another inherent problem (like bad glue lines from wood cupping when TB III touches it).  Tillering and belly slat selection are far more important.

[Hamish]

The ultra light wood core concept becomes more a problem with shear(as has already been mentioned) and also the potential for work hardening fatigue, which is not good for longevity. ie a light core(from softwood, or a very low density hardwood) will give good performance until it fails. Timber like yew is a good compromise(hardest of the softwoods)yet still light, or bamboo flooring/panelling lamelles.The  old stand by of maple suggested by PatM performs well, not too heavy, but still strong. They will all still give good performance, but failure is very  unlikely due to shear.