I think just heat treated . They do poplar too .
I just wondered if it was too brittle for a riser but I guess amberboo is heated too
Heat treated bamboo vs natural bamboo definitely increases the deflection and compression strength, and is preferable in bow laminations. But the flexible nature of the bamboo itself is till there.
But heat treating Ash and poplar is definitely going to make it brittle. It may work just fine for a riser if it can hold up to the shock. They didn’t have any technical specs on elasticity, or hardness, or mass weight density that I found.
I’d say give it a test run on a 65# bow and dry fire it a couple times. That will tell the tale right there…. Kirk