The federal government requires that sealed containers with contents that can't be measured without destroying the package be labeled with the net weight. Aerosols are packaged this way. The net weight is the measure of the content and propellant less the packaging weight. Solvents commonly used in brake cleaners vary in weight across a broad spectrum, especially with chlorinated solvents such as Perchloroethylene (aka. Perc, Tetrachloroethylene, TCE) and Methylene Chloride (MCL). A given fluid amount of Perc weighs more than the same fluid amount of MCL. What this translates to is that some same-weight aerosols containing higher amounts of Perc, or all Perc, have less fluid content that the like size of a packaged filled with Perc. The higher the fill of MCL in relation to the Perc, the more liquid in the container, such that some 19-20 net weight containers could have less fluid in the can. Add to the content the superior cleaning power of MCL and you have higher quality and could have more quantity, such that the difference in price may be completely offset with performance and volume. FACTOID: WHEN PICKING UP A CAN OF BRAKE CLEANER, HOLD IT IN THE PALM OF YOUR HAND AND SLOWLY ROCK THE CAN BACK AND FORTH TOP TO BOTTOM. THE CAN SHOULD SEEM TIGHTLY PACKED. IF IT FEELS AS IF THERE IS SOMETHING SLIDING END TO END INSIDE THE CAN, THEN THE THE CONTENT OF THE FLUID IS HEAVIER. TRY IT WITH #1420. THE CAN SHOULD SEEM FULL. THEN COMPARE LABELS AND LOOK FOR METHYLENE CHLORIDE AS AN INGREDIENT TO INSURE THE BEST PERFORMANCE.