For optimal efficiency, a base filter to block IR is required to use with the NB2 and NB3 series IDAS filters. The IR spectrum will leak into your images otherwise.
The IDAS Nebula Booster 2 filter series is excellent for those who already own a filter to block the IR spectrum and especially those with a double-stacked filter drawer on their setup. The NB2 filters boost the signal for OIII and Ha wavelengths to get that perfect image you're looking for.
The graph below shows the wavelengths of the NB2 paired with the IDAS NGS1 filter in a dual-slot filter drawer.