Uncoupling and waterproofing membrane.
Brand New about 1/2 of a 323 sq ft roll.
Link to Schluter website for information:
https://www.schluter.com/schluter-us/en_US/Membranes/Uncoupling-(DITRA)/Schluter%C2%AE-DITRA-&-DITRA-XL/p/DITRA
Floor and Décor, see link below:
https://www.flooranddecor.com/s/floor-decor/shower-systems-installation-materials/schluter-ditra-uncoupling-membrane-951503087.html