Some foods are bottled when they are hot such as catsup and must be bottled in polypropylene containers. Polypropylene would be less likely to melt upon microwaving. Yogurt also comes in polypropylene containers since they are heated to high temperatures. Permanent storage containers are generally polypropylene. Polypropylene had a high melting temperature allowing it to be used with hot foods.
Polypropylene is also very strong.