Difference between emitter and absorbers

An emitter allows things to pass through a surface from inside to outside.

An absorber allows something to pass through it from the outside to the inside.

Shiny surfaces are poor absorbers and emitters (but they are good reflectors of infrared radiation). If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object. This is one reason why domestic radiators are thin and flat.