These are high-density blocks balsa wood that can be charged with abrasive pastes for the purpose of sharpening straight razors.
Razor Strop: Wide, Single Sided Balsa Strop With Diamond Paste
Homemade Balsa Wood Strop.
Balsa Wood Strop
Stropping with green compound versus diamond paste
3 razor strop varieties.
Leather strop with balsa wood, boxed. 3 varieties including Russian Foal
Diy Basswood strops cheap and easy! : r/sharpening
Stropping - balsa vs basswood
Balsa wood razor strops
Stropping, Angles and Dumb Luck – Wicked Edge Precision Knife Sharpener