Dark brown calfskin leather + lined strap

This watch strap is a dark brown color, with the following characteristics:

II. Material Analysis
Based on the images, the strap is most likely made of:

1. Outer Material: Top-grain cowhide

2. Lining Material:
Microfiber leather lining
PU lining
Genuine leather lining

3. Buckle Material:
The buckle is a gold-plated metal buckle, typically made of:
Stainless steel + PVD gold plating
Advantages:
Rust resistant
Moderate cost
Good color brightness