Economic history of technological change in the British iron industry from 1700 to 1870, drawing on firm-level records to trace the diffusion of new ironmaking techniques through a framework of incremental profitability rather than discrete invention. Hyde’s central finding — that adoption rates correlated with the cost advantage of new methods over existing ones, rather than with the availability of the technology itself — is a durable insight about industrial transitions: the bottleneck is rarely technical feasibility; it is the economic conditions that make adoption rational for individual operators. Relevant to any analysis of how new industrial processes spread, including decarbonisation technologies.