This study investigates how network traffic is affected by passing through a transparent firewall, focusing on packet loss under saturated and unsaturated conditions. The tests are performed on Cisco ASA with Firepower image and Fortinet Fortigate 40F in transparent firewall mode. To measure the performance impact, Iperf3 is used to generate traffic and Wireshark is used to analyse packet loss. The results provide insight into how transparent firewalls handle traffic flows and whether they can be a bottleneck in a performance-critical network.