Bitumen, the binder used in Bitmac, comes in a range of “penetration grades”. There are specific tests that determine just what is the “penetration grade” of a given bitumen, but, rather than go into a lot of very technical and insomnia-curing detail, it is best to think of ‘pen’ as being a measure of “bitumen softness”, of how far a point load will sink into a block of pure bitumen at normal temperatures.

The pen grade of the bitumen binder has a direct bearing on the ‘hardness’ of the bitmac produced using that bitumen, and so we have a range of penetration grades, from 15pen, which is pretty damned hard, to 450pen, which is relatively soft. A ‘softer’, more pliable binder produces a softer, more pliable bitmac. Imagine trying to push the blade of a Phillips screwdriver into a bitmac surface; some bitmacs will offer far more resistance than others, and a lot of that difference is dependent on the ‘pen grade’ of the bitumen binder. So, some bitmacs are harder, or softer, than others, and the degree of pliability can be tailored to suit the requirements of the job in hand.

Colordrives only ever uses SMA surface course which is 125pen this is the lowest pen that can be specified for hand laying tarmac, some less respectable contractors will use a much higher pen grade which will mean they have much longer to work with the tarmac, but will result in a finished surface which is to soft and will be very easily damaged by car tyres.