I. Sources of Odor in Slippers
There are two main sources of odor in slippers. The first is residual foot odor left behind by feet with foot odor, making the slippers a victim of circumstance. The second source is the odor emitted by the slippers themselves, which can be categorized into two situations: one is a foul smell emanating from the slippers even before they are worn (due to poor-quality materials), and the other occurs after wearing them for a while when they begin to emit an unpleasant smell.

II. What Kind of Slippers Are Less Likely to Harbor Bacteria?
The likelihood of a slipper becoming a breeding ground for bacteria mainly depends on its materials and manufacturing processes. In other words, slippers that resist odor must remain clean and dry (not absorbing water or sweat and not trapping dirt) or possess special antibacterial properties.

In the images provided, the two pairs on the left are made from PVC, with the upper layer being softer and the bottom layer being harder. On the right are EVA slippers, with the thicker bottom layer being softer and bouncier, providing that so-called "squishy" feel. It’s clear that the same material can yield different properties based on manufacturing processes.

The semi-transparent hard plastic slippers at the bottom (the older style crystal slippers) are less prone to odor compared to the PVC ones because of their manufacturing process. They are solidly molded, making them hard and smooth, which prevents water accumulation, sweat, and dirt. However, the PVC soft plastic slippers, which have a foamed texture and air holes, are more prone to absorbing water and odor, often becoming sticky when worn. Some vendors mislead customers by selling these foamed PVC slippers as EVA slippers because of their slightly lower production costs (though the price difference is minimal).

III. How to Choose Non-Odoriferous and Safe Slippers
Here are some simple tips:

Avoid slippers with any odor or those with added fragrance; some manufacturers use recycled materials and may add perfumes to mask unpleasant smells.
Be cautious when selecting PVC materials, especially foamed soft PVC slippers, as they are likely to contain recycled materials and excessive plasticizers.
If you don't mind a firmer feel and comfort, consider traditional crystal slippers or rubber slippers, which are currently among the least odorous options.
Overall, EVA slippers are the best choice—economical and comfortable. The cost difference between EVA and PVC is not significant, so it’s worth spending a few extra dollars on a pair of simple, comfortable EVA slippers. There's no need to skimp and buy PVC ones, but ensure you purchase from reputable manufacturers or brands, as subpar sellers may use inferior materials (like recycled materials) or misrepresent products (selling foamed PVC as EVA).
There are no slippers that are absolutely odor-free; foot hygiene, sweating, and proper maintenance (keeping them dry and clean) all play a role. Normally, EVA slippers should remain odor-free for about a year. Over time, material aging can cause dirt to accumulate deep within the slippers. Fortunately, EVA slippers are affordable, so when the time comes, simply replace them; there’s no need to splurge on expensive house slippers—unless you’re a luxury buyer.