TDBU stands for Top Down Bottom Up. It’s an optional feature (not a control type) that lets you lower the blind from the top — maintaining privacy while still letting light in — and you can also raise it from the bottom as normal as well
In the true sense of TDBU, you can have the blind positioned in the middle of the window — with clear glass both above and below at the same time. TDBU is available with corded, cordless (SmartRise), and motorised honeycomb blinds
If you’re choosing cordloop, the comparable option is Top Down (TD) — covered in full in this FAQ — which gives you top-down control, but it doesn’t allow the “floating in the middle” setup that true TDBU does
