Making a window seat cushion

[GlueSticksEverywhere]

Hi I want to make a cushion for a window seat. What do I use for the filling? Do I use upholstery foam?

I've been googling on how to do it and it keeps mentioning boxing material . . . what's that then? I assumed I'd just buy some fabric I liked and would cover it with that but most places mention the fabric and the boxing material.

I think boxing just means the "gusset" of fabric around the edge that gives the cushion its 3d shape, it's an upholstery term like "piping". So for say an oblong cushion you'd cut a top, a bottom and a long (or joined lengths) strip of "boxing" maybe three inches deep all round the edge. It's all the same fabric. quite often the zip is set into the boxing i.e. side. Take one of the seat cushions off your sofa and it should make sense

Oh really? I was thinking maybe it was some sort of lining fabric.

Boxing material is like a thicker interfacing type of material. You can then put a netting type of material that goes over that. What it does is round off the hard edges of the foam to give a better/comfier seat.