i make hot pads and potholders a lot. i use batting or fleece batting along with insulbrite as the inside material and 100% cotton fabric for the shell fabrics. i would not use poly synthetic fabrics for the shell as they are highly flammable.
i purchased insulbrite for $2.47/yd at hobby lobby. it was much more expensive at joann's and hancocks. i heat test them before i send as gifts.
there are so many free online patterns for potholders and hot pads. have fun with making these. they make great gifts.