Is the word snowflakes a common noun?

Yes, the Word snowflakes is a common noun, the plural form for the singular snowflakes, a Word for any snowflake anywhere.

A proper noun is the name of a specific person, place, thing, or a title; for example:

• "Ken Libbrecht's Field Guide to Snowflakes" by Ken Libbrecht
• Snowflake Lake, Kenai Peninsula, Alaska
• Snowflake Bentley Gift Shop, Jericho, VT
• "Snowflakes" a comic strip by James Ashby, Chris Jones, and Zach Weiner
• "Susie Snowflake", 1916 movie with Ann Pennington, Leo Delaney