Normal double glazing units do not have a vacuum in them and the seal is there to stop moisture getting in there. There is no reason why you cannot have a custom unit made with a hole suitable for a catflap. The glass used in glazing units is toughened by heat treatment after being cut (it is very difficult to cut once toughened) so you need to have the hole put in before the glass is toughened, as it is possible to get double glazing units with extractor fan holes in them so it should be possible to have one with a catflap hole. I would suggest a supplier of "glazing units" off e-bay.There are two other approaches that would work:1) To use glass that is not toughened but instead achieves its strength through lamination (layers of glass and plastic), that is laminated glass, which can be easily cut by your glazier and then assembled into a unit with seals around the catflap opening.2) To use polycarbonate instead of glass with holes cut in it and assembled into a unit with seals.I would suggest trying the glaziers in Actons before the opposite the small green (next to Twyford School) on the south side of the Uxbridge Road (if it is still there), it is a long time since I used it, however, I found Allbright somewhat pricey.Phew, that required thought.
Mark Julian Raymond ● 2701d