The price is per Sqm.  

This vapour layer is required for installation of Smart Flex over all concrete floors.   If concrete floor the relative humidity is over 93% a further treatment will be required.  

Instructions - Unroll the underlay with Silver damp-proof membrane side up. Lay the first and last underlay rows with a 2cm flap up against the wall which then can be covered with a timber skirting. To join please use a waterproof tape - https://www.danceandstage.co.uk/accessories/single-sided-tape-for-joining-vapour-membrane 

Thickness is 2mm