"Ultra-refined" fish oil is very different from standard over-the-counter fish oils. First, it is a concentrate of fatty acid ethyl esters as opposed to fatty acids assembled on a triglyceride backbone. This change in molecular structure is necessary to be able to refine the oil, which removes the toxic contaminants found in all fish oil. This complex refining process also significantly increases the concentration of the long-chain omega-3 fatty acids.
​ 
This change in molecular structure creates other noticeable differences. First, ultra-refined fish oil flows like water compared to a typical oil. This increase in flow improves the incorporation of ultra-refined fish oil into the cell membranes that line the intestine. Typical fish oils must be broken down by various enzymes before the fatty acids can be absorbed, which is an inefficient metabolic process for many (which prevents any real benefit). However, ultra-refined fish oil can also penetrate into porous surfaces, such as plastic. Therefore, you should exercise caution ultra-refined fish oil comes into contact with any porous surface, as prolonged contact can actually potential damage such items.