My loft has old insulation bags installed between the rafters. Can't be more than 100mm thick. I see that the general recommendation is for minimum 300mm.

Does anyone have any experience of a cost effective source for insulation? Are their cheaper options than Bau-Hobby/Jumbo. I guess that the soft fibreglass insulation would be far easier to install than the hard foam that seems to be prevalent in new builds. Anything else to consider?

Thanks in advance for sharing any experience

Cheers
Jekyll