There are two main things that can be found in the DPF. Formed by the incomplete combustion of fuel, you’ll find carbon-based soot which can be burned away through regeneration. You will also ‘ash’, formed from metal-based impurities caused by burning small amounts of engine oil. This slowly builds up over time in the DPF and, unlike soot, this ash cannot be burned away through regeneration.
After about 100,000+ miles, eventually the ash could build up to the point that the DPF needs to be cleared out. This means an external filter clean or a complete DPF replacement. This timescale maybe reduced however if there is an oil system problem or the wrong type of oil is used.
A common claim is that sometimes DPF Additives that contain FBCs should not be used as they will lead to the DPF clogging up anyway by contributing to the ash.
This is true to a certain extent, as the metal oxide from the FBC is deposited in the DPF. But as long as the normal recommended dose from the supplier is followed, then in general it only contributes to a small amount of ash when compared to the standard build up due to the oil.