If he goes to USPS.com it clearly states that in order to be declared a package it must be either RIGID, NOT UNIFORMLY THICK OR NON RECTANGULAR. It says nothing about 3/4" thick. You can print that page and take it with you. If you want to mail them in a regular envelope, keep it under 1/4" with cardboard and just pay .20 cents for rigid surcharge. Or to save arguments, like I do, the retired mailman, just buy the stinking .88 cents at the counter, walk outside and put it on and drop it in the mailbox outside.