It doesn't inflate to 4 inches and I've followed the instructions as stated.   I may return this if my sheets don't fit and try to find something else.  The platform mattress that we ordered from you  didn't inflate to the 8 inches that it stated and I don't know how we could get it back into the box it came in to return. That is the reason that I ordered this mattress topper hoping it would help the mattress gain the 8 inches that I need so my sheets fit.  I'm disappointed in both items that we ordered.