Ms Thunberg told Vogue Scandinavia that fashion brands needed to take responsibility for the environmental impact of their products.
In a tweet, she accused some companies of "greenwash" ad campaigns designed to make their clothes appear sustainable.
Vogue Scandinavia featured Ms Thunberg, 18, on the cover of its first issue.
In the interview, Mr Thunberg said she last bought a new item of clothing three years ago and "it was second-hand".
"I just borrow things from people I know," Ms Thunberg said.