Premise: It is more expensive than the run-of-the-mill Century line of car seats (a Britax runs above $200), but it is made of material so hard it would crack your knee if you walked into it, and its belting system is far more encompassing and elaborate than the average car seat's.

Hypothesis: The quality of this car seat is superior, hence it's a bit more expensive than others. 
Relation: entailment