My winter camping has been limited to cold camping in December and early March, my sleep system has been ok for temps 0 and above. For tarp, overnight camping in Jan. and Feb. I have been thinking of adding my DIY cot pad for more insulation and comfort; the pad is 1.5" memory foam in a cover. ( it began life as a home queen mattress pad). It worked great as a cot pad at 20 /40 degrees. It will be on top of a reflecting pad and a Thermarest Ridgerest pad. I don't want to spend money on winter specific gear, since it only for a hand full of nights a year. Great idea? Bad idea? Anyone ever tried it before?

My little research I did indicates it is closed cell foam you are using so it should help your sleep system. Still, I think you could use more under you. I find the ground can really suck the warmth out of you if you don’t have enough insulation between you and the ground.

You really want the reflective pad closest to you. So I hope you do so.

Memory foam gets stiff in the cold. When I leave my house (outside of Ely) for extended periods in winter I close off my bedroom from heat. My memory foam mattress is like a pool table when I climb into sleep. As my heat warms it I make a soft area in the shape of my body. When I switch sides I don't fit in the indent.

Yup Banksiana is right.

Memory foam is possibly the worst thing one could use in the winter. It will freeze and will steal heat from your body as it warms up. I used memory foam in my roof top tent in October and was miserable.