Hi Vanchat,
I would echo Jeff’s comments that the smell of a mattress is a separate issue from the level of harmful VOC’s that may be coming from a mattress (some harmful VOC’s don’t have a smell).
There are also several certifications that test for the level of harmful VOC’s but the certification only identifies whether the mattress is under the testing limits for that specific certification and doesn’t “rank” them relative to each other or specify which are “best or worst”. There is more about the different “safety” certifications in post #2 here but again I would keep in mind that there may still be an odor to a mattress that has passed a safety certification. Any odor would normally be stronger at first until the mattress has a chance to air out and some people may be much more sensitive to certain smells that other people may not notice nearly as much.
There is a lot more information in post #2 here and the more detailed posts and information it links to about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and answer “how safe is safe enough for me” that can help each person decide on the types of materials they are most comfortable having in their mattress or on the certifications that may be important to them. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices.
If you are purchasing a mattress online that you can’t test “or smell” in person before a purchase and you have specific criteria about smell or anything else that are important to you then the return/exchange policy would become a more important part of your purchase just in case a mattress doesn’t work out as well as you hoped for or in case you are sensitive to the smell regardless of whether the materials have a certification.
Phoenix