"The sole of a shoe, also known as the outsole, is the bottom part of the shoe that comes in direct contact with the ground. Shoe soles are made from a variety of different materials, including natural rubber, leather, polyurethane and PVC compounds. The material used to make the sole depends upon the style and purpose of the shoe."

The yellowing is part of the shoes (rubber, plastic, icy soles, white midsoles, boosts) natural oxidation process that results from exposure to air, you can’t totally prevent it from happening. 

How to remove yellowing on soles:

The best way is through those "sole sauce" bottles that is sold on the internet.  We are/used to unyellow soles for sneakers. Our Rem's Sole Revitalizer works well. Our customers/clients used it on a pair of ultraboost's with mild yellowing, and it got back to white within 1 session of 30 mins - 1 hour. Shoes with mad yellowing, like Jordan 11 Space Jams, will obviously take longer or just be improved. It all depends how you store it.

 BEFORE USING REM'S SOLE REVITALIZER

AFTER USING REM'S SOLE REVITALIZER (2 SESSIONS OF 1 HOUR EACH)

Just be aware that the midsoles/soles CAN get yellow again. Properly store the shoes by leaving it in the box, taking out the paper (accelerates yellowing), and placing a silica packet inside the box.We hope this helps, thank you for your reading!