Kinetic sand is a mix of 98% fine sand and 2% polydimethysiloxane (a silicone oil which sounds scary but is apparently used to reduce the froth in deep-fat frying and making jalapeno poppers!) so is considered non-toxic.
Its advantages are its ability to be heated to high temperatures without any change and to retain its shape for moulding without sticking to the object in question. With the impression of the item made in the sand, it is possible to fill the impression with a range of molten materials such as wax, low-melting point metals and even glue gun glue!
It seems that it should be possible both to use textiles and other materials to make impressions for casting but also to embed textiles and other materials within the molten liquids.