This is the current nylon filter according to their site. [1] REI says polyester. [2] According to this study steeping coffee with a polyester pouch emitted lots of microplastics. [3] Steeping is different than a pour over. However, it's still hot water passing through the nylon|polyester for a few minutes. [1]: https://gsioutdoors.com/products/ultralight-java-drip [2]: https://www.rei.com/product/784659/gsi-outdoors-ultralight-java-drip-coffee-maker [3]: https://www.sciencedirect.com/science/article/abs/pii/S0308814623003345.