What is the difference between the Boveda Directional Holder and other Boveda Holders?

The Boveda Directional Holder is exclusively for acoustic instruments on display that have a central sound hole, such as an acoustic guitar or ukulele.
A vegan leather barrier on one side of the holder creates a capped seal over the sound hole, so the water vapor in Boveda can interact with the wood of the instrument body while it is out of its case and on display.

Conversely, the other Boveda Holders can be used with any wooden instrument while it’s inside its case.
Both sides of each holder allow for water vapor to flow in and out and throughout the instrument case.