Yes, "supper" is a closed syllable. A closed syllable is one that ends with a consonant, which is the case with "supper," as it ends with the consonant "r." The first syllable, "sup," also follows the closed syllable pattern, as it ends with the consonant "p."
Closed
It's a closed syllable.
Yes it's a closed syllable.
It is a closed syllable.
Paper is a closed syllable word.
Yes.
Closed
Closed
It's a closed syllable.
It is an open syllable.
It's a closed syllable.
It's a closed syllable.
Yes it's a closed syllable.
Swim is a closed syllable.
It is a closed syllable.
Yes it's a closed syllable.
First syllable closed, second syllable open.