Mar Omega is the creator of this brilliant technique for creating spiked wooden barricades* for LARP games. They're painted pool noodles. The one detail that isn't pretty self-explanatory from the image is how to get the paint to stick. Pool noodles are made from polyethylene foam and almost nothing will bond with the plastic permanently. At a guess I'd say they're coated in spray on Plasti Dip or truck bed liner.
*Technically they're Cheval de frise, but that doesn't roll of the tongue nearly as well as "spiked barricade".