Bird Nest Starter Material is a natural wood fibre that matts together and provides an extremely well insulated base layer in all types of nest box.
Insulating and natural wood fibres can also help improve nest box occupancy rates. By placing a few cm of wood fibre in the bottom of the nest box the birds' natural instinct to ‘spring clean’ its chosen site is triggered prior to nest building. You will likely see birds busily removing a proportion of the material prior to bringing in new nest building materials such as grass stalks and feathers etc. and this is an entirely normal process.