In the wake of the report of a fatal accident at Mallory (See bikes forum) I was asked just what a Recticel is. Whilst it's not strictly marshaling related (untill the buggers get loose!) I shall put the answer here.

A recticel is a great big lump o' foam. It's put in front of banks, walls and other solid and inanminate objects (including armco) with the express intention of stopping motorbikes. Acting like a tyre wall but solid so you don't get tyres everywhere.

see Here

Not to be confused with tyres covered in conveyer belts, as favoured by F1 Circuits.

Basically the idea is to absorp the energy of something moving very fast!