These shoes are cheap compared to the NB 623s I currently wear for Pickleball. The upper is made of soft synthetic material and has a small area above the toes with slits for ventilation. I sweat a lot and I'm sure the shoes will collect sweat in a thin insole. I bought on ebay but it was a third party sale so it cost me $12.60 to return. Reviews exaggerate the quality of these sneakers. I will no longer buy from a third party on ebay due to the cost of returning shoes. Reasons for return: 1) QUALITY DOES NOT MATCH 2) I DID NOT LIKE THE PRODUCT, 3) THE APPROACH WAS TOO SMALL.