Thanks for the help chaps – though I’m not sure I’m any the wiser. Googling everybody seems to say along the grain of the outer sheets is stronger, but I’m not sure if standard ply has thicker outer sheets.
ernie – I’m just asking whether it’s strongest along the grain of the (thin) outer ply, or along the grain of the (thicker) ply underneath that. Sorry for complicating things!
I also appreciate it’s not strong in an absolute sense, but I’m assuming significantly stronger than the 3mm MDF I was using before. It’s for use as the top sheet on a jump ramp for my 5yo – generally well supported, but ~7cm gaps between the supports which the ply spans between. So not major structural stuff. I figured 5mm was thick enough (actually sold as 6mm and I was expecting 5.5 as that seems to be the standard) given that I do need to be able to bend it to shape.