MDF/HDF ( medium/high density fiberboard)  made by converting wood chips into fibers, then mixed with glues , pressed into required sized. 

Features: easier for sanding, shaping, polishing and painting. high density ensure strong screw holding capacity. 

Application: 5mm MDF for cabinet back panel , 9mm MDF for drawer back panel, 18mm MDF used for doors. 

HPL ( higly pressed laminted particale board) made by converting solid wood into chips, then mixed with glues and pressed in to shapes. compared with MDF, melmaine surfaced HPL board has stronger screw holding capacity and more water proof. 

Features:  more stronger screw holding capapcity, more moisture resistant. 

Applications : differenct melamine colors laminated , 16-18mm HPL for carcasses.