When choosing a cheap waterproof fabric for a hospital mattress cover, there are several factors you should consider:

1. Waterproof: The fabric should be completely waterproof to protect the mattress from spills, stains, and moisture. Look for fabrics that are specifically designed for waterproofing.

2. Breathability: Choose a fabric that is breathable to allow air to circulate and prevent the buildup of moisture, which can lead to mold and mildew growth.

3. Durability: Look for a fabric that is durable and can withstand the wear and tear of regular use and frequent washing.

4. Comfort: Consider the comfort of the fabric for the patient. Look for a soft and comfortable fabric that will not irritate the skin.

5. Size: The fabric should be the appropriate size to fit the hospital mattress. Check the dimensions of the mattress and choose a fabric that will fit properly.

6. Ease of cleaning: Choose a fabric that is easy to clean and maintain. Look for fabrics that can be machine washed and dried.

7. Price: Look for fabrics that are affordable and fit within your budget.

Overall, when choosing a cheap waterproof fabric for a hospital mattress cover, it is important to consider waterproofing, breathability, durability, comfort, size, ease of cleaning, and price. By taking these factors into account, you can select a fabric that is suitable for your needs and provides reliable performance.