Donaldson Company (DCI) describes itself as a "tech-leading" air and liquid filtration business. That description is not far from the truth. One of the appeals of Donaldson as an investment idea is its "razor-blade" business model, which is driven by its investments in R&D to create proprietary products and winning contracts with OEMs early in the design stage, leading to a sticky replacement business afterward. The company's proprietary products also lead to a higher-margin business compared to a more commoditized filter replacement market, contributing to higher returns on capital. Donaldson's return on invested capital