I just want to double check how to test memory foam density. If I understand correctly, the density is the weight per cubic foot. If I multiply the length x width x thickness of the topper I will get the cubic inches. I then divide that by 1,728, which is the number of cubic inches in a cubic foot. Is that correct?
So for a California King topper, I would multiply 72"x84"x2" (the thickness of topper), which gives me 12,096". Dividing that by 1,728 gives me 7. So a California King topper 2" thick would be 7 cubic feet. Am I on track so far?
If I’m looking at 5.3lb density memory foam in a 2" CK topper, it should be 37.1 lbs according to this calculation.
4 lb memory foam would be 28 lbs.
3 lb memory foam would be 21 lbs.
Second part of my question is, how accurate are the density numbers that are given? Are they exact or just a rough guide? What would be the normal range of fluctuation?
The density will normally be in a range of about 5 - 10% or so depending on the tolerance when the material was ordered (tighter tolerances cost more) and there could be some slight variations in the dimensions as well. Sometimes descriptions will be rounded off as well (described as 4 lbs when it’s 3.8 or so) so they should be reasonably close but not necessarily exact.
Thanks, Phoenix, I thought that was how it worked.
I ordered a 5.3 lb Cal King memory foam topper 2" thick and received it today. I slipped it out of the box without unwrapping it, weighed it, and it comes up 27.5 lbs. By the calculations above, it should be 37.1 lbs.
The description of the topper says it is cut to the full size of the mattress.
I wouldn’t mind if it was off a little bit, like the up to 10% you mentioned, but this seems a bit much. At what point does 5.3 lb become 4 lb.
There could be some variation in the dimensions that could account for a small part of this but if the weight is accurate then this would be about 3.93 lb/ft3 (not taking the wrapping into account) which is clearly not 5 lb memory foam.
I would definitely call the supplier and ask “what happened?”
Many customers are shopping for the best price these days. As retailers feel the price crunch, some retailers in order to compete and beat everybody prices are selling 4 lbs foam and passing it off as 5 lbs. Very few people will verify the density of their toppers, and for the ones that do, the retailer will usually simply exchange the topper to keep the customer happy. We suggest buying your foam from a reputable company that is buying his foam in North America in order to get what you paid for.