High-density Polyethylene foam is made by the material LDPE resin with high density(ranges from 30 to 300kg/m3), the higher density of the foam, the harder it is.
With the high density, it is usually used in places which need excellent strength, such as the floor underlay, construction, automotive back trunk, etc....
Here is the datasheet of our polyethylene foam which is cross-linked closed cell foam type.