According to this US Postal Service page http://postcalc.usps.com/Postcards.aspx?m=8&dz=76710&oz=76710&dpb=0&mdt=2015/04/21%2000:00
, the maximum thickness (calliper) for small postcards at standard rates is .016 inches. I would like to find either A4 or 8.25 inch x 11 inch glossy paper that matches that thickness. Those sizes can both be simply quartered to make the mailable postcard sized advertisements. Most paper is measured in gsm (grams per square meter or g/m2) which appears to be 102.1 gsm. Assistance in finding an inexpensive resource with the highest thickness is greatly appreciated.