I pulled the liner out of my Nolan Helmet today and soaked it in the laundry tub in a mixture of Baby Shampoo and water.
It was pretty grimy so I left it to soak and forgot all about it for most of the day.
The baby shampoo has soften the glue that kept the foam pieces attached.
I want to glue the pieces back on, but I don't know what kind of glue to use as I'm afraid of melting the foam.
The foam insert came loose in my 1/2 helmet so the shell moved around independent of the liner on my head. As I remember I used Liquid Nails to put the foam liner back in the shell and it has not moved in a couple of years or so.
Go to an automotive supplier like NAPA and buy some upholsery spray adhesive and follow the instructions. It will not melt your foam and will not feel lumpy like liquid nail.
If you do not want them glued in permenant. Go to a fabric store with hobby supplies and get a fabric spray it will make your lining tacky yet will come back out.
A thin film of contact cement on each surface should do the trick.Let it set up a couple of minutes and put them together.Make sure the foam is located corrctly before you stick it to the helmet,because it isn't moving afterwards.