I use a Cokin SFX filter with infrared film. This is an old filter, and it seems a little different from the current COKIN CREATIVE – Infrared Filter 720 (89B). For a start my SFX filter is a gel, and I am not sure the 89B is. Also I have measured mine and I think that it has a filter factor of 8 stops. Where the 89B is listed as 6.
The filter is circular in a plastic holder so it is a little hard to use with wider angle lens, the filters can get into the shot. So in these cases I tend to use it without a holder. Just holding it over the lens myself. The other thing to be aware of is that you really can’t get it wet. That knackers it.
You can see the sort of pictures it produces in my infrared gallery. I have also included one below.