Cups: 100% natural, biodegradable Lid & Sleeve: Silicone. With natural insulation properties keep your drink warmer for longer. Completely dishwasher and microwave safe. Rice Husk is the brown outer shell that rice comes in and is an agricultural waste. Annually the worlds rice production is approximately 500 million tonnes. Of this the ratio of tice husk to rice is approximatley 1:4, which is usually incinerated. At the end of its lifespan, your rice husk cup can be buried in soil, becoming part of nature again.