Semipermeable membranes are of diff types depending on the type of solute present in soln ,mainly it is formed keeping in mind pore size of solute particles still research is going on to prepare more efficient S.P.M. S.PM generally means a membrane not allowing solute under cosideration to pass through it .u shud keep in mind that parchment paper r not truly S.P.M for e.g S.P.M for is obtained frm cellulose acetate or frm aromatic polyamide (aramid) .For dialysis parchment membrane is used ,for simple osmosis films of gelatinous ppt e.g cupricfeerocynide used as S.PM for sucrose