Aerosols have advantages in areas where the pump system has obvious limitations. Whenever the subject of spraying comes up, pumps have often been advocated as a “a spray option”. Pump technology is well-known as the forerunner of the aerosol principle. So the question of whether to use aerosol or pump isn’t so much a general decision as a product-based one. The pump system doesn’t allow even distribution of the product and will only let you apply it in moist form. That's absolutely fine for some applications – but not for painting. The argument that pump vessels contain 100% active ingredients cannot be supported, unless you count solvent or water as active ingredients. That's because, unlike sprays, pumps do not form the classic “aerosol” (suspension of fine particles in the air), but dispense irregular, moist-to-wet clouds of active solvent. In addition, pumps cannot guarantee consistently high pressure until the can is finally emptied. Because of these technical considerations, paint is best applied using a classic aerosol can.