This is Sphagnum Moss that has been compacted in a block. This block needs to be rehydrated. This moss is a live moss and will keep growing under the right conditions when watered but not when dried. It can be used for hamster, reptiles & plants. 
This moss is great for top layers of bedding & nesting, creating natural environment, filling any gabs from wooden items and decor. 
The bag in the picture is how much you get after you rehydrating and drying out fully. Bag in picture measures 42x30cm (quite a large bag) 
If you are using this moss for hamsters make sure you fully dry it before placing in the enclosure/play area. You can dry it in the oven at low temperature or air dry it. Make sure you lay it out thinly to dry so there is airflow. 
We have recommended instructions for rehydrating this moss at the back of each pack.