than carbon dioxide because the latter is soluble in water finally encapsulated bubbles can be embedded in the gel during its formation conventional 34 blister pak 34 can be used on the top and bottom of the gel as barriers therefor or embedded in the gel as shown in fig3 a b at 50 alternatively a plurality of transparent plastic balls 51 can be cast in place in the gel in each case the trapped bubbles enhance the insulating effect of the gel the method of preparing an aqueous gel from the acrylic monomers is exemplified by the following examples which are not considered as limiting mixtures of 2 3 composition were prepared using 20 g of acrylamide 0 6 g methylene bisacrylamide 0 625 g of aps in enough water to make 1 liter stirred into the solution is 0 063 ml of temed all the constituents being at ambient temperature 20 u00b0 30 u00b0 c each mixture gelled in about 2 3 hours when exposed to sunlight if kept in the dark about 60 of the mixture gelled and the balance remained as water a mixture like that of example no 1 was prepared but 200 g mgcl 2 6h 2 o were dissolved before the temed was added after two hours at 22 u00b0 c the solution gelled in the dark to a clear firm gel a mixture like that of example no 1 was prepared but 5 g magnesium chloride 6h 2 o was dissolved before the temed was added the solution gelled at a temperature of 27 u00b0 c but an ungelled layer of 2 millimeters remained on top of the clear.