The function raydium_ode_element_slip() (
http://wiki.raydium.org/wiki/RaydiumApiReference#543) can be used to add a certain material behaviour to an element.
Here the different slip type pre-defined in Raydium:
#define RAYDIUM_ODE_SLIP_ICE 5.f
#define RAYDIUM_ODE_SLIP_PLAYER 10.f
#define RAYDIUM_ODE_SLIP_NORMAL 0.4f
#define RAYDIUM_ODE_SLIP_DEFAULT RAYDIUM_ODE_SLIP_NORMAL
Also you can modify the ERP and CFM (more complex way) to get your custom behaviour with raydium_ode_element_material (
http://wiki.raydium.org/wiki/RaydiumApiReference#541)
These are the raydium pre-defined values (from ode.h)
#define RAYDIUM_ODE_MATERIAL_HARD 0.9,0.1
#define RAYDIUM_ODE_MATERIAL_MEDIUM 0.5,0.5
#define RAYDIUM_ODE_MATERIAL_SOFT 0.1,0.9
#define RAYDIUM_ODE_MATERIAL_SOFT2 0.0,0.9
#define RAYDIUM_ODE_MATERIAL_DEFAULT RAYDIUM_ODE_MATERIAL_HARD
So for example you can set an element like
raydium_ode_element_material(element,RAYDIUM_ODE_MATERIAL_SOFT);
or a bit more soft, but not as soft as soft2 with:
raydium_ode_element_material(element,0.05,0.9);
The best way is try-out