I’d suggest looking for these quality checks while buying plywood.
Core Gaps & Overlappings: Shouldn’t have any core gaps (small gaps in between layers of core). Look for these in the side profile along the length & breadth of a panel. It should look like the layers running straight in parallel lines without gaps. Ask for full core panel plywood made with full core and not “Falli”. 1mm – 2mm gaps allowed intermittently for a couple of instances. Anything more than that compromises the structural integrity of the panel. Shouldn’t have too much overlapping of these layers of plies while composing. The lines of different layers on the side profile of plywood should be running straight. If they overlap each other too much, its not good.
Weight: Higher the weight of the ply, better its density, and therefore better its strength and performance. A normal full red core plywood of Eucalyptus timber make should weigh 39+Kgs for a 19mm 8×4 Plywood Sheet. A alternate grade plywood made of alternate layers of Eucalyptus and Poplar timber should weight around 32+ for a 19mm 8x4ft Plywood Sheet.
Prefer Eucalyptus (red Core): There is a myth that Gurjan is the most premium wood we should use. Its not. It has a slightly higher density but it doesn’t have any tangible edge over Eucalyptus when it comes to performance but costs a hell lot more! Eucalyptus gets the job done and serves the purpose your ply is intended to do for a lifetime. So instead of buying really expensive Gurjan(not available in Indian anymore, imported from Burma), go for Eucalyptus core.
Nail Holding Capacity: The strength of a plywood panel is predicated on its capacity to hold a nail while being used in furniture. Before buying a ply, ask your dealer to hammer in a nail (1.5inch #14) into the side profile of a plywood sheet. If the layers split or crack on nailing, the bonding isn’t strong enough and will not work for furniture work.
Test reports: Any genuine manufacturer would have factory lab test reports as well third party test report of their plywood panels. Ask for these from the dealer before purchasing. A good manufacturer generally also offers guarantee on the panels, ask for a certificate if they have one.
Choose Correctly: Lastly buy according to the purpose you need it for. For indoor furniture, which isn’t going to come in contact with water much, use MR grade (moisture resistant), for any furniture which has a chance of getting in contact with water often such as kitchen furniture, use BWP(boiling water resistant) / Marine Ply. You can test a marine ply for its waterproof characteristic by taking a cut sample and boiling it in a pressure cooker for 7 whistles. The layers of the ply shouldn’t delaminate in a genuine as per standard marine ply. If it splits, its probably not a marine ply.