I used to wake up everyday with aches in my neck and lower back. I am only 30 but I felt like I was 90, all crotchety and stiff. I was involved in a serious car accident and have always needed 15 pillows to find comfort even when sitting up. I am exaggerating but you get the point. I always hurt. We had purchased a new pillow top mattress thinking that would help. It was quite firm and I did not want to deal with the hassle of finding another expensive failure. I resorted to these toppers. I purchased 2 of the Slumber Solutions Highloft Supreme Memory Foam toppers in the standard King size (one 3" and one 4"). I couldn't decide after reading the reviews so I bought both....If you are trying to decide between the 3" and the 4" Let me help you out. READ THIS. Both had a smell...nothing to run away from...just a little like fresh rubber and Pine-sol. Most of it went away by the 2nd day. Surprisingly the 4" was less smelly than the 3". Let me tell you - There is a HUGE difference between the softness/squishyness between the 3" and the 4" heights although everything else is the same (density, size, etc). The 3" provides cushion but nothing ultra plush. It provides extra comfort but you can still feel the hard bed through the bottom of the topper. The 4" is the ultimate in comfort. It is super thick and you CAN NOT feel the hard mattress underneath. I was able to put the 4" on the floor and not feel the floor. You could feel the floor through the 3". I never would have thought that 1" would make that much difference but IT DOES! It is unusual because the 4" is soooo soft but yet my back doesn't sink into a hole. I tried it with the fingers up and with the fingers down and I prefer them up. I feel like they are holding me up everywhere they touch my body -back of the neck, shoulder blades, lower back, even the back of my legs, hammys, and calves.. I didn't think I would like it. I have never been an egg crate kind of gal but this is different. I absolutely love to cuddle into my bed and rub my feet back and forth giving me a little massage right before I drift off into bliss. ...I guess this is what people mean by sleeping on air. I never understood them or what they meant when they said that. It is really nice. I seriously ask my husband every morning "How did we live without this?" He agrees. We have never had so much comfort out of an item that cost so little. I needed soft cushion with good support and the 4" is the answer. Both the 3" and the 4" are GREAT products and I would recommend both. We use the 3" king -cut into 2 twins- for my 3 year old son and also the guest bed. Both beds were hard as cement and it was actually nicer to sleep on the floor before. Topper sizing was perfect standard King makes 2 twins- just cut with sharp scissors. Now with the toppers they are quite comfy. My son no longer climbs out of his bed to sleep on the floor. My guest also commented that his bed was tremendously more comfortable too. He slept on the bed before the topper arrived and then after I placed it on the bed. NIGHT AND DAY DIFFERENCE> So, in conclusion, if you are trying to decide between the 3" and the 4" and you are looking for squishy, supportive comfort GO WITH THE 4". If you need to save a few dollars then go with the 3" but I can almost guarantee that you will wish you had spent the few extra dollars for the 4" right after you receive the 3”. Do yourself a favor and do it right the first time…BUY THE 4” TOPPER.