Proper leather shoes

Did you mis type something? Good shoe trees hold form but shouldn't be put in when the shoes are damp? I assume you are aware of what happens when leather absorbs moisture.

Correct. Its a bit counter to what the high street shops might suggest.. but talk to George Cleverley, John Lobb and Edward Green, All three London shops will, I think, give the same advice. The general rule of thumb is to wait at least 2 hours before using the tree--- if the shoe is particularly moist it might need a longer wait. Since the function of a tree is to form the shoe, you want to wait for the shoe to stabilize before you insert them, You absolutely don't want to stretch the shoe, especially when damp. The second rule of thumb is that once the trees are inserted one should wait at least 48h before wearing the shoes again.