What makes double sided business cards effective for marketing?

A second side turns a contact card into a small ad without costing much more.

• The back can hold a promo offer, a portfolio link via QR code, or a short service list.
• People naturally flip cards over, so the back message gets seen with no extra effort.
• Two sides double your usable space for both identity and offer.
• Consistent design across both sides keeps it looking intentional, not cluttered.