纸张 is a formal term for "paper," often used when referring to paper as a material or product category. While 纸 alone also means paper, 纸张 is more commonly found in written or formal contexts, such as listing materials or products.
这家工厂生产各种纸张产品。
zhè jiā gōngchǎng shēngchǎn gè zhǒng zhǐzhāng chǎnpǐn.
This factory produces various paper products.
打印之前请检查一下纸张的大小。
dǎyìn zhīqián qǐng jiǎnchá yíxià zhǐzhāng de dàxiǎo.
Please check the paper size before printing.
回收纸张可以减少对环境的污染。
huíshōu zhǐzhāng kěyǐ jiǎnshǎo duì huánjìng de wūrǎn.
Recycling paper can reduce environmental pollution.