What do you call that white material used to reinforce the cloth being sewn?

.
Liner or fabric lining? Buckram?
.

Thank you. Buckram is the word I was looking for. There are many other reinforcing materials. What is a general term for them?

What search phrase should I use to google those materials?

.
I don't know any good ones; my search to answer your question was not a very satisfactory one, all in all-- I remembered that the word started with 'B', but all I could think of at first was 'burlap'. I googled ''fabric lining" at first, I recall, and then wandered from that point.
.

It's okay, Mr Micawber, at least you tried. I'm sure you will remember that word soon. So I'm waiting.

Can I say: I'm sire you will remember that misplaced word soon?
You have that word somewhere in your mind but at present you couldn't recall it because your memory recollecting device doesn't exactly know its location.

.
No, the word was 'buckram', and I finally found it in my search and gave it to you; only then did my mind recall it. But I have no bright ideas on searching related words, if that was what you asked above.

I'm sure you will remember that word soon.-- This is fine.
.