Short answer: A narrow network is a smaller, curated set of providers that lowers premiums by steering you to lower-cost, higher-value doctors and hospitals. A tiered network keeps a broad list but charges you less to use ‘preferred’ (Tier 1) providers.
Insurers control costs partly through network design. A narrow (or ‘high-value’/’select’) network contracts with a limited set of providers in exchange for better rates, which lowers the premium; the trade-off is fewer in-network choices. A tiered network is broader but sorts providers into cost tiers: you pay the least for Tier 1 (preferred) providers and more for higher tiers, nudging you toward efficient ones without excluding the rest. Either way, check that your preferred doctors and hospitals fall in the network (or the better tier) before enrolling.