Abstract This paper explores the scientific sources behind Kant’s early dynamical theory of matter in 1755, with a focus on two main Kant’s writings: Universal Natural History and Theory of the Heavens and On Fire. The year 1755 has often been portrayed by Kantian scholars as a turning point in the intellectual career of the young Kant, with his much debated conversion to Newton. Via a careful analysis of some salient themes in the two aforementioned works, and a reconstruction of the scientific sources behind them, this paper shows Kant’s debt to an often overlooked scientific tradition, i.e. speculative Newtonian experimentalism. The paper argues that more than the Principia, it was the speculative experimentalism that goes from Newton’s Opticks to Herman Boerhaave’s Elementa chemiae via Stephen Hales’ Vegetable Staticks that played a central role in the elaboration of Kant’s early dynamical theory of matter in 1755.