i knew someone was gonna say that.

anyways, any other suggestions while keeping the coffee WITHIN the cup?

 

I wouldn't sleeve the inside of the cup, because aluminum foil conducts heat, so your coffee will get colder.

 

It doesn't say the the opening has to be a certain diameter does it? If not the take the cardboard make a second cup but 1 cm bigger(in diameter and dept), line the outside of the Styrofoam cup in aluminium, shinny side facing in. Put Styrofoam cup in the bigger cup and fill will foam chip.
If it must be practical and you must be able to drink out of it, the don't fill the gap with foam all the way up, bend the 2 edges together and tape.

Or the other way arround woul be better, cardbaord inside and styro cup out insde, but not quite sure how to make the coffe stay in carboard, unless lining the inside of that one with platstic wrap, then i would be just like a styrofoam cup but thicker!

 

foil conducts electricity, hide a battery in the inside and use the foil as a heater coil :naughty:

 

yea, the top has to be 7cm in diameter and i dont think i can use an extra cup nor a battery, lol.

thx guys, keep them suggestions coming.

 

Well with my option the diameter would be 7cm but the thickness of the rim would be 1cm, so still not bad! and you would make a cup out of the cardboard provided, no extra cups. lining the inside with foil would be useless, its so basic that the warmt would really be kept, what you need it to isolate! and best way for that are layers! 1-styrofoam 2-foil 3-foam 4-cardboard!