'My pyjamas are of silk' is a very acceptable English expression
Made of, maybe, but just 'of' is at the very least uncommon if not awkward.
do we really need the 'made of'?
No, and it is accepted without "made of".
Mine was not accepted; 'of silk'
"Made of silk" is standard and accepted. Plain "silk" is standard and accepted. "Of silk" is colloquial and evidently not accepted.
neither was mine
why not "made from silk"?
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. :-)
Now I understand too the meaning of "pair of scissors". (You need one scissor for one garmet) ;-)
Why not 'my pajamas are of silk?' Does it not convey the same meaning?
"my pyjamas are of silk" is perfectly good English, & should be accepted.