Frontier does not accept human remains for shipment.
NOTE: Crematory remains (human or animal) may be transported under certain conditions. The container must be made of a material such as wood or plastic that can be successfully screened by the Transportation Security Administration (TSA). TSA will not open the container under any circumstances. If the container cannot be screened, it will not be allowed. If the urn is checked, it must be sufficiently packaged in a well insulated and sturdy container.
Here is a list of all acceptable items that are considered for baggage & carry on items.