Made of, maybe, but just 'of' is at the very least uncommon if not awkward.
Why not singular "pajama"? I think "- Pyjama-s" - is plural? Anyway, in German it's like that, and I think in English the end "s" is also used for the plural. What exception is made here?
I think I found the answer on my question for myself: English names all trousers in plural becose they have two legs (trouser's; pant's; pyjama's). I wondered because they do not the same with the shirts? There are eqal two arms ;-)
Pants at one point used to be made of two separate garments (one for each leg), hence you would wear a pair of these garments: a pair of pants. Shirts did not originate as a pair of garments. :-)
Interesting. Thanks. Now I understand too the meaning of "pair of scissors". (You need one scissor for one garmet) ;-)
'My pajama is silk,' marked incorrect by DL, is correct English in my area --- NYC. Pajama for singular, pajamas for plural. Perhaps it is a localism but I would guess at least 50 million Americans would accept it.