Cotton Insulation vs Glad Wrap Bag for solar water heater?

[lasisdabomb]

Hello Physics Forum. I have to complete a solar water heater project for school and choosing between what would be better for the insulation of a tin reservoir. I'm leaning towards the glad wrap bag because it will let more light hit our reservoir. However it will be a quite windy day and cotton might better suited for this type of conditions.

 

[DrGreg]

Hello Physics Forum. I have to complete a solar water heater project for school and choosing between what would be better for the insulation of a tin reservoir. I'm leaning towards the glad wrap bag because it will let more light hit our reservoir. However it will be a quite windy day and cotton might better suited for this type of conditions.

Can you think of an experiment that you could try, to decide which is best?