The breathable ground sheet just like the Bolon will allow mud slurry to seep though if you are in puggling about conditions so I doubt that is the reason; possibly it could be to help alleviate any stone damage on a more aggressive hard standing pitch?Morganic said:I have just purchased an Isabella Bolon Breathable Groundsheet for my awning. The supplier recommends the use of a breathable underlay. Is this necessary?