Upholstery fillings

[sewmuchmore]

I am going to reupholster my settee/chairs again but want to replace the back cushions with something softer. At the moment they are a shaped piece of foam, which were disintegrating last time i recovered them so dread to think what they are like now if i take of the covers.
Any ideas of what i could use instead? What are the seats/backs of  modern sofas filled with? And any suppliers you can recommend?
I have used E-Foam before for the seat pads and will probably replace the seat pads using foam.

[Greybird]

@sewmuchmore I think most of them now are filled with foam but of course there are many grades of foam and now include memory foam. There are several online suppliers who would probably be able to recommend which are most suitable. They are often wrapped though with wadding which makes the surface more comfortable and softens the shape. Mine are supposedly covered with a feather filling, but I imagine the feathers must be contained in some sort of cover (like a thin duvet?) otherwise they would all sink to the bottom wouldn't they?