thick, thin
leather, rubber
inner

the sole of your boot, the sole of your shoe
There's a hole in the sole of my shoe.

the soles of your feet
The sand was so hot I got blisters on the soles of my feet.

Sole is used with these nouns:
aim, author, charge, command, criterion, custody, discretion, distributor, exception, explanation, focus, heir, means, motivation, object, occupant, owner, ownership, possession, prerogative, proprietor, province, purpose, reason, reliance, representative, responsibility, right, stockholder, supplier, survivor, trader, trustee