United States SCHLUTER®-KERDI-SHOWER-FRS inserts must be made from plywood subfloor panels at least 23/32" thick, with a span rating of at least 19.2" and an Exposure 1 bond classification or better. OSB is not permitted. Panels that typically meet or exceed this requirement include 23/32" APA Rated Sheathing with a 48/24 span rating and Exposure 1 bond classification or 23/32" APA Rated STURD-I-FLOOR with a 24 oc rating and Exposure 1 bond classification. To verify compliance, look for the APA trademark on the face or edge of the panel. When buying online, check the product description, specifications, or technical data sheet for the panel thickness, span rating, and bond classification. Canada SCHLUTER®-KERDI-SHOWER-FRS inserts must be made from CSA O325 plywood panels at least 23/32" (18 mm nominal) thick, with a floor span mark of 2F20 or greater, as specified in the installation instructions. A separate Exposure 1 bond classification is not required, because CSA O325 plywood is manufactured to CSA O325 bond durability requirements. To verify compliance, look for the CSA O325 grade stamp on the face or edge of the panel. When buying online, confirm the panel thickness and floor span mark (e.g., 2F20, 2F24, or 1F32) in the product description, specifications, or technical data sheet.