Introduction Most cigarettes are smoked with filters made of synthetic plastic, which are not fully biodegradable. Littering used cigarette filters (butts) represents a substantial environmental hazard. It is unclear if people, in particular smokers, know that filters consist of synthetic plastic.

Methods We used data collected in August/September 2019 from a representative household survey of the German population aged 14 years and over (wave 20 of the German Study on Tobacco Use; DEBRA). Respondents were asked: ‘The majority of smokers use cigarettes with a filter. What do you think these filters are composed of? (1) Mainly of natural material; (2) Mainly of synthetic material; (3) I don’t know what cigarette filters are composed of.’ Response option 2 indicated correct knowledge.

Results A total of 2066 people were interviewed, including 625 current smokers. The weighted response rate to option 2 (‘mainly of synthetic material’) was 34.8% (95%CI 32.7 to 36.9) in the total sample and 42.7% (95%CI=38.7 to 46.8) in the subgroup of current smokers. In the latter subgroup, smokers with low compared with those with high educational level were less likely to know that filters are mainly composed of synthetic material (OR=0.62, 95%CI=0.39 to 0.99).

Conclusions The majority of smokers in Germany does not know that cigarette filters are mainly composed of synthetic material. Our findings suggest a need for promoting awareness as well as knowledge of environmental health hazards of cigarette filters to the general population, and specifically to current smokers.

Trial registration number DRKS00011322 and DRKS00017157.