Bich became extremely wealthy thanks to his invention, which had worldwide appeal. Over the next 60 years his company, Société Bic, opened factories all over the world and expanded its range of inexpensive products. Today, Bic is as famous for its lighters and razors as it is for its pens, and you can even buy a Bic mobile phone.

The word "which" in paragraph 4 refers to ________.