I've been trying to gather more information about the thickness of early playing cards. This is a crucial question when attempting to re-create early playing cards so I've gone to some effort. I have contacted multiple museums and conservators and been fortunate enough to have some responses. The Beinecke Library, in particular, was exceedingly helpful. I am still in awe of the amount of work they did in response to my request. Most of my requests are still outstanding but I hope to receive more responses this month.
The summary is: Playing cards were constructed of a smooth, white paper made from hemp and linen. In early playing cards this paper was between 0.17mm-0.24mm thick with 0.19mm-0.22mm being the most common range. This equates to a paper weight of approximately 199gsm (plus or minus a few grams). Cards were constructed of multiple layers of cards, in most cases, which gives weights of 400gsm to 800gsm. With modern cards being produced in a range of 290gsm to 320gsm you can see that early playing cards were much thicker. As time went on card makers became more sophisticated and began producing cardstock using a thick (0.22mm to 0.26mm) paper for the core and thin paper (0.11mm) for the face and back.
An interesting note on this research is generated by the Morisca Cards held by the Fournier Museum. This museum deserves some credit as they are, so far as I am aware, the first to take a thickness measurement of cards in their holdings and publish those measurements. And those measurements are interesting because they reveal the Morisca cards are, at their thickest, 0.18mm thick. This is, of course, nicely within the range of of other measurements. What's interesting is that the Morisca Cards appear to have survived as cards rather than as portions of a binding. That might indicate the Morisca cards were made from a single sheet of paper rather than from two or more sheets. The provenance of this deck is unclear and I've written the museum requesting more information but have not, as yet, heard back.
I'll add more information as it becomes available.