It's the least expensive 5mm or 6mm rubber underlayment I can find. Rubber Underlayment is what I've decided on after researching cork vs. rubber underlayments. I'm still open to other suggestions though.
I will be doing either floating floor or glue down floor. I will not be nailing or screwing down the flooring.
The bamboo is real bamboo flooring. It's not engineered or fake.