Very thin; flimsy. Can describe something physically thin or, figuratively, shallow or superficial (e.g., shallow arguments or character).
この本の表紙は薄っぺらくてすぐ破れそうだ。
The cover of this book is flimsy and looks like it will tear easily.
彼の説明は説得力がなく、薄っぺらい印象を与えた。
His explanation lacked persuasive power and gave a superficial impression.
薄っぺらい素材のコートは冬には向かない。
A coat made of thin material is not suitable for winter.