Following a request from the European Commission, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP Panel) was asked to deliver a scientific opinion on the efficacy of a preparation of algae interspaced bentonite when used as aflatoxin B1 (AfB1) binder for all animal species; the additive is composed of bentonite feed grade and algae belonging to Ulva spp. The European Commission request follows an opinion of the FEEDAP Panel published in 2016; in that opinion, the FEEDAP Panel could not conclude on the efficacy of the additive. The applicant has submitted additional information to allow the FEEDAP Panel to complete its assessment; these additional data, related to the efficacy of the additive, are the subject of this opinion. In the efficacy study provided, the use of the additive reduced the AfM1 in milk, although this effect seemed to be not consistent over time; this study presented some weaknesses and limitations (incomplete data analysis, reporting and lack of determination of the active substance of the additive in feed) which do not allow the FEEDAP Panel to draw any conclusion on the efficacy of the additive. Due to insufficient evidence, the FEEDAP Panel cannot conclude on the efficacy of the algae interspaced bentonite as a technological feed additive for all animal species