Why the threads matter more than the coating
Everything depends on the threads being the same length and densely enough spaced. Where they are, the two faces cannot bow apart and the panel stays flat under pressure. Where thread density is low, the surface quilts visibly between anchor points and the panel loses stiffness. Thread density is therefore a specification in its own right, separate from base fabric denier and coating thickness — and a supplier who quotes only a gsm figure is hiding all three.
It cannot be added afterwards
The two faces and the connecting threads are produced together on a specialised loom or knitting machine, then coated. There is no process that turns ordinary coated fabric into drop-stitch after the fact. That is why the mills making it are a distinct and fairly small group, and why buying the fabric is a different supply conversation from buying tarpaulin.
Where the commercial range sits
Commercially available chamber depth runs roughly five to thirty centimetres, which covers paddleboards, inflatable boat decks, gym mats and most shelter walls. Requirements outside that band are unusual and should be confirmed with the mill before anything is designed around them, rather than assumed available.
What it is not
Drop-stitch is not the same as air-beam construction, where a few large inflated tubes act as a frame with fabric stretched between them. Both are called inflatable, and they behave very differently when something punctures. If you are comparing two quotes, establish which construction each one is before comparing anything else.