First of all, carapils is a crystal malt and should be treated as such (keep the % low in your grist- a pound is a lot unless it's the only crystal in your recipe).
Second, it's really a bandaid for other problems that may be causing poor head retention (recipe formulation, process issues, water composition). Consider Chimay White, a tripel which is just pils malt and sugar- massive everlasting head.
Third, it's more expensive than flaked barley, which will give you way better head retention anyway, add mouthfeel, contribute fermentable sugars and not sweeten your finished beer.
So, in conclusion: look to your recipe/process/water first if you're not seeing what you want. Then if you want even more head or rockier foam, try some flaked barley!
PS: this is primarily for all-barley beers. Rye and wheat also add some nice proteins which contribute to head retention.
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