In this article, a cross-disciplinary approach is used to create an overarching theory of how and in what ways plastics are forming an archaeological record. By drawing on foundational archaeological research into those cultural and natural site formation processes that shape the archaeological record, a new theory of site formation in the contemporary ‘Plastic Age’ is presented. This theory is also relevant for predicting future archaeological records. In both cases, the type fossils are not stone, metal, or ceramic, but plastic, creating an archaeological record that is resilient and toxic, as well as ubiquitous. Over time, this contemporary archaeological record is increasing exponentially in overall size, while its component parts (the artefacts) continually break down, eventually to a nanoscale. This presents a contradiction: how society should view an archaeological record that represents a valuable archive documenting activities and behaviours at a crucial time in human history, while at the same time being a dangerous contaminant, threatening planetary health. In conclusion, the article argues the need to reassess what is meant by ‘the archaeological record’ and how it is formed in the Plastic Age—for example, by working more across disciplines to better understand what this archive is telling us about ourselves and about the future.