Hung explains that the drying must be done in the dark. If you get anxious and expose the head to sunlight, the fabric will dry on the surface but still be damp underneath; then if you rush to put on the second layer, the fabric will deform later on.
洪來旺強調，布胎一定要陰乾，絕對不能貪快用日光曝曬，否則表面乾燥，但內裡的棉布纖維並未乾透，若急著上第二層，日後就會變形。