Greaseproof paper is paper that is impermeable to oil or grease and is normally used in cooking or food packaging. Normally greaseproof paper is produced by refining the paper stock and thus create a sheet with very low porosity. This sheet is supercalendered to further improve the density, creating a paper called glassine. The glassine is treated with starches, alginates or CMC in a size press to fill pores or treat the paper chemically to make it fat repellent. Basis weights are usually 30-50 g/m².