Formaldehyde is used for most synthetic adhesives, which are used for wood based composites production. Part of formaldehyde is bonded and part remains unreacted. Unreacted formaldehyde slowly emits from board. Due to high water solubility, formaldehyde is rapidly absorbed into the human body. For many years now, the wood - processing industry has been trying to increase the quality of products and thereby to reduce emissions from wood based composites. The key factor at emission of formaldehyde is related to surface from which formaldehyde can emit into environment. Impact of exposed area on emission were measured on particle and fibre boards which were surface treated with impregnated melamine - resin paper. We used paper with surface weight 130 g/m2 and 200 g/m2 . Edges of the particleboard were closed with melamine tape and aluminium tape. The emission of free formaldehyde was measured by a gas method according to the SIST EN 717/2 standard. We came to the conclusion that surface treatment is crucial in reducing the emissions of free formaldehyde from plate composites. By processing the panels' edge and surface, the emissions can be reduced by 90 %.