I’m confused by all this talk of high flow and low flow! What’s the difference?
Now this is the most contentious issue in water-cooling and has been the cause of many a flame war on various forums but I will do my best to explain the differences in as open a manner as possible.
High flow, (also known as large bore) is traditionally associated with American water-cooling companies and is typified by the use of ½” (internal) diameter tubing and powerful pumps.
Low flow (also known as small bore) is favoured by the European (mostly German) water-cooling companies and refers to their preference for 6-8mm (internal) diameter tubing and less powerful pumps.
So which is better? This is the contentious issue. To all intents and purposes they are the same. They both cool your components well and to within a few degrees of each other. High flow systems do have the performance edge but you have to match components carefully and make sure there are no restrictions, which will hamper performance. It is also unsuitable for multi-block systems where lots of components are being cooled. Low flow systems are more forgiving to the beginner and are extremely flexible allowing lots of components to be cooled within one loop.
Water Cooling FAQs - WizD Forums
To a certain extent there is now a convergence between the high and low flow philosophies with the general consensus that 3/8” or 10mm diameter tubing gives the optimal performance. The development of pumps designed specifically to meet the needs of water-cooling has also changed water block design and lessened the difference between the two.
A post by Cathar, a person who has been one of the main driving forces of PC water-cooling, discussing the merits of different diameter tubing can be found here.