Hi Mary, 
 
Thanks for your question. 
 
We don't retail any sort of memory foam ourselves so can't comment definitively.
 
Generally the foam on the underside will be firmer than the top layer and as such we wouldn't really recommend using the underside. 
 
Our safest advice would be to contact the retailer you purchased from to seek their advice. 
 
If you have any further queries please don't hesitate to contact our office on 0161 437 4419.
 
Kind Regards, Lee.