Apparently, for a better fit there is a process to custom fit the slides. I didn't do this, but the here are the directions:
Step 1 .Prepare a hair dryer. Put on 2 pairs of regular socks
Step 2 Use the heat of the hair dryer to soften the upper for about one minute. Make sure that the air outlet is about 10-20 cm away from uppers.
Step 3 Put on the slides immediately and wait for 3-5 minutes, the slides will naturally shrink to fit your feet.
Step 4 Repeat steps 2 and 3 for the other slides.

From the manufacturer:
The deep heel cup and concave vamp with roomy toe box wraps around the whole foot absorbing impact to protect your toes safe
Built with 1.7 inch thick sole enhance cushioning
Designed with anti-slip textured style the slides prevent foot slipping and falling as well as coming out
Thick slides concise style and solid design perfects for all season and occasions, bathroom, indoor bedroom, living room, swimming pool, outdoor beach, holiday, spa, leisure, public showers, steam rooms etc.