Summary
It is - a man-made object, a household item, with a practical use.
It is not - one word, a natural feature, double-glazing, powered, a container, used at mealtimes, used in the construction of a house, aertexed ceilings, mainly metallic, decorative, something to do with interior decoration, something to do with reading.
flerdle owns more than one of it, and something like it was in use over a thousand years ago, but its modern form is the answer.
A question about cosmetics is outstanding.
Is it some form of clothing?

[Irouléguy] I suspect that "flerdle owns more than one of it" may be a misunderstanding. I interpreted flerdle's response to mean that it's a thing which doesn't usually have number, such as wallpaper (although interior decoration has been ruled out).

[Darren] hmmm... No.
[Irouléguy] No.
[Darren] Your interpretation is correct. And no, it's not wallpaper.

[Rosie] No.

[Tuj] No.

[Raak] No.

[Raak] Yes
[CdM] Yes

[INJ] No

I'd call soap vegetable (possibly veg/animal) but that's me. Still worth asking.

Darren] Thanks - well spotted.

[Darren] No.
[Darren] Still No.
[Raak] No.
[Kim] No.
[Irouléguy] YES it is indeed dental floss; remember, you don't have to floss all of your teeth, just the ones you want to keep.
I was hoping more of its qualities would come out but it was a race through the bathroom that got it in the end, thanks to CdM's astute observation. hmmm...

Over to Irouléguy

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ah, just too slow... I thought of toothpaste first, but realized it suffered from the one-word problem, and so went for my general question instead.

Sorry for the delay, y'all - I'm off work so only switching the computer on intermittently. So, our answer is ABSTRACT. No colour clues, but with a connection to tomorrow's elections.
CdM] Is it a Higgs boson? No
Darren] Is it something you'd want to show your friends? Possibly