The opening is a bit narrow but fits into typical sonic gel bottles or squeeze tubes of massage cream (which is what I've used them for). But slightly larger lotion/oil bottles, such as B. a separate electric oil heater, are not suitable. If it were a bit wider it would fit in 8oz cobalt blue glass pump bottles and I would give it 5 stars. (Glass is MUCH easier to wash off of oil/lotion and doesn't warp with heat!) This is the size I was looking for and I can't seem to find a heating pad that fits! It doesn't make the oil/lotion too warm, it just soothes the chills! But that's a good thing, too, because you don't want to denature your food with too much heat. Overall I am happy with my purchase and using it.
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