What to Look for in Diesel Exhaust Fluid

When you’re shopping around for diesel exhaust fluid (DEF), you’ve probably noticed that all the diesel exhaust fluid suppliers claim to have the best product on the market. It’s true that not all DEF is the same, so it’s important to know how to choose the best products from all the DEF suppliers out there. Here are some tips to help you find the right product.


DEF is mostly made of a urea concentration and water. The right mixture of urea and water is essential in order for the fluid to work with catalysts and go through the SCR process to turn the nitrogen oxide into harmless water, nitrogen, and oxygen. This reaction is what lowers emissions and makes it possible for EPA emission standards to be met. For DEF to qualify as such, it must have 32.5 percent of pharmaceutical grade urea (NOT agricultural grade urea) and 67.5 percent de-ionized water.  These percentages are determined by weight. This exact makeup is critical because it provides the lowest freezing point possible at twelve degrees Fahrenheit,and also provides the best NOx reduction possible without affecting the vehicle’s performance or driving power.

ISO Standards

Another qualification that DEF must meet is the International Organization for Standardization (ISO) specifications. ISO standard 22241-1 not only monitors the concentration of the DEF, but it also determines the production, handling, and transportation of the fluid. The standard also outlines how the DEF should be stored and distributed.  

Impurity Levels

Another aspect of the ISO standard is the level of impurities in the fluid. Maximum levels of zinc, iron, aluminum, and copper are specified. These levels are very low, and DEF can’t contain anything above specified levels, because anything higher than these levels negatively impacts the SCR performance. 

API Certification

If you find a product on the market claiming to provide SCR but it’s not marketed as DEF, chances are high that the product is just a urea solution that was unable to meet the requirements for ISO certification. In addition to looking for DEF products that are ISO 22241-1 certified, you can find a quality product by looking for the American Petroleum Institute (API) certification. This certification is voluntary, so it’s possible that not all DEF has this certification, but purchasing from diesel exhaust fluid suppliers that have API certification ensures the DEF is high quality and meets ISO standards. 

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