The Southwest Africa Medal (Südwestafrika-Denkmünze, sometimes abbreviated SWA) was awarded to Imperial German forces service in German Southwest Africa in 1904 to 1908. 

 The Southwest Africa Medal original silk ribbon (most original issues were made in Berlin) varies in width from 3cm to 3.2cm (depending on the maker).   The various ribbon types have notes which are of interest to the collector.  

• Contemporary Ribbon:  Silk, the weave is 16 rows per cm, each thread is 2 strands of ca. 12 fibers per strand, and it is UV-negative.  Silk, the weave is 17 rows per cm, each thread is 2 strands of ca. 10 fibers per strand, and it is UV-negative.  The vast majority of these ribbons are 3.0cm to almost 3.2cm in width.
• WWI-era Replacement Ribbon:  Silk, the weave is 15 rows per cm, each thread is 2 strands of ca. 20 fibers per strand, and it is UV-negative.  Silk, the weave is 16 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative. 
• WWII-era Replacement Ribbon: Silk, the weave is 15 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative.  Cotton, the weave is 14 rows per cm, each thread is 2 strands of ca. 10-12 fibers per strand, and it is UV-negative. 
• Modern-era Replacement Ribbon: Often found in widths of exactly 3.00cm, 3.05cm, 3.1cm, or 3.2cm.  Silk, the weave is 14 rows per cm, each thread is 3 strands of ca. 10 fibers per strand, and it is UV-negative.  Cotton, the weave is 13 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative.  Poly, the thread melts and clumps when burned, the weave is 15 rows per cm, each thread is 2 strands of ca. 10 fibers per strand, and it is UV-positive.  Cotton, the weave is 14 rows per cm, and each thread is 3 strands of ca. 8-10 fibers per strand.  Note that some of these ribbons have a false UV-positive due to the use of a fabric finish. Poly-cotton mix, the weave is 14-15 rows per cm, each thread is 2 strands of ca. 10-15 fibers per strand, and it is UV-positive.   

My best advice is:  Buy only from a reputable dealer who specializes in Imperial German medals.  Please visit my blog (http://blogs.ebay.com/tsa-li) and/or guides for further information.  Thank you for your visit!