Ok heres some industry research facts, from a guy in plastics :-
Timber boards are porous. Anything on t he surface that is slightly fluid will 'wick' into the board. Oiling Reduces but does not totally stop this.
in some instances, more dependant on the bacteria than on the wood, bacteria can actually grow / reproduce. Cleaning, oiling disinfecting can limit this, Choice of wood can also help limit this for a while, but eventually any anti-bacterial properties in the woods oils will be washed away.
Glass boards are impervious to moisture. that means there is no retention of bacteria in the boards surface. If there is any bacteria remaining afterwards it's
because of the quality of the cleaning regimen.
Glass boards surface is extremely rough on a microscopic level, making them hard to clean well. They are also quite damaging to knives.
Plastic boards should only be made from Polyethylene. Many other cheap plastics are used but not considered safe for direct contact with food. PETE (Poly Ethylene Terepthalate - also known as PETP) is Not a food safe material once it has been in contact with temperatures greater than 65 degrees as it may swell trapping moisture. Nylon falls into the same category. PVC can leach stabilisers into fluids. Polyproylene is food grade depending on TYPE, which they never tell you. recycled plastics should never ever ever be used as they may contain voids, allowing fluids to be trapped.
Plastic boards have a relativley smooth impervious surface, which doesn't damage knives. However, knives can damage the surface of the board, creating pits and scores in which food residue can be trapped. If, after cleaning, any bacteria remains on a Plastic board, it's
the quality of cleaning which is a problem,
or the plastic used.
Suffice it to say - there are only 2 materials allowed in industrial and commercial food processing plants, for direct contact with food. Stainless steel (grade 306 only) and Virgin Polyethylene (usually specified as High Density Polyethylene - HDPE).
Of course there are specialty plastics that work as well. Virgin PTFE, POM, UHMWPE etc, but they are not as cost effective, so you don't see them.
The easiest way to test this for yourself is very simple. Get one of each type of board. Drop a single drop of food dye in the middle. Rub it well into the board with a finger. Rinse off quickly. Check to see which one has least dye in place. That is the board that absorbs least and releases most contaminants - of any sort.
By the way Do not trust any information published on the web from Specific plastic manufacturers. Companies like DOtmar EPP and similair often market their specific product under the banner of a plastic type. There version of a product such as ERTALYTE, which is a type of PETP, is not necessarily the same PETP someone else may be talking about. It's based on PETP yes, is it pure PETP - no. Plastics is a confusing industry