The material used in so-called “survival filters” is a material the water filtration generally calls carbon block. Depending on the manufacturer and the sales process carbon block is the most common filtration media used in disposable filters. This would include refrigerator filters, faucet filters, various pitcher devices and the survival filters that you mentioned.
It must be pointed out however that carbon lock is not ceramic, and scientifically speaking is not porous in the manner you are noting. The materials used in carbon block are indeed porous, but microscopically so. The actual pores are not visible to the naked eye. The porosity that you refer to is really a coarseness to the touch that occurs as a result of compacting the filtration material and adding plasticizers and binders to it.
So now, to answer your question as to what the actual material is.
As a general rule of thumb, the types of disposable filters we are talking about are made up of 70% or more of Granular Activated Carbon (GAC). Gac is ground down to 100 mesh size or smaller, at times as fine as powder. At that point, additional media such as ion-exchange resin, zeolite, or silver particles (bacterial control) may be added to come up with a proprietary/customized filter.
Once the media is all mixed together the substance is processed through the introduction of plasticizers, binders, and molding to deliver a final product. It is the granular nature of the pulverized media combined with the solidification of the chemicals that cause the final product to feel like a porous, ceramic material.