Chuánglì sì jiǎo yǒu sōngjǐndài, tào shàng hěn fāngbiàn.
A fitted sheet has elastic at the four corners - easy to put on.
Tips
usage
床单 = flat sheet that you tuck under the mattress; 床笠 = fitted sheet with elastic that wraps the mattress like a 笠 (bamboo hat). Modern Chinese bedding sets often include both, but the 床笠 has become the default lower sheet.
