Hi ,I would not recommend insulating wallpapers on a high traffic area like a stair case especially if you have children or pets .
I have used the graphite wall liner in my box room as it was extremely cold and had the original wallpaper peeling,one wall being a gable end .
It does work ,the room is now warmer and I have no issues with condensation.The problem is it's a pain to apply and takes a lot of work .
I would think it would be a nightmare and rather expensive to do a stair case wall with long lengths.
My aim is to insulate the wall as it's cold. I've used the polystyrene wallpapers before and the insulation is surprisingly good. I'm wary of using it on the stair wall though because it could easily get dented so I am looking for an alternative.