Oriented strand board is an excellent alternative to plywood provided it is woodmarked and sourced as locally as possible.
The word ‘oriented’ refers to the fact that the strands (or flakes) of wood are slightly more orientated along the length of the sheet than across it, making it slightly stronger (in tensile strength) in that direction.
Greenpeace have recently come out with a report about how unsustainable much of the plywood is that is imported into the UK, and how OSB is an excellent alternative. Below is an extract showing where OSB can be substituted for ply along with cost comparisons
Table 1. Sustainable alternatives
This table shows where illegal tropical hardwood plywood is typically used and the responsible alternatives available in the UK. All FSCForest Stewardship Council (who accredit timber) see their database OSB available in the UK market follows the CE2+ standard. FSC Marine Plywood follows the BS1088 standard.
FSC Tropical Hardwood is also an available alternative.
Prices (in 2010) are for standard 18x1220x1440mm sheets, other than Marine Plywood, which is
for 9x1220x1440mm. Prices are per sheet when buying one pack of sheets. Prices vary
according to the quantity purchased and availability.
T>ongued and grooved (as with floor boarding) OSB for flooring is available but can take some finding.
The European Panel Federation publish a guide to OSB including technical information