I'm looking to get myself an infrared filter to put in front of my lens. The cheaper ones all have nm counts (like 720nm, 950nm, 1000nm, and the way I understand this, the thicker, the better), but there also are more expensive filters, like hoya r72 ect, and it is never explained, why they are 3+ times more expensive than the brand-less filters.

Is this only because of the brand, or is there something more to infrared filters?