Green Building Advisor has a great article on understanding R-value and avoiding insulation scams.
Here is an excerpt of this article:
“Some marketers of radiant barriers or spray foam insulation imply that R-value measurements are meaningless. On the contrary, R-value is a useful measurement. But just because you know a product’s R-value doesn’t mean you know everything necessary to predict heat flow through a wall or ceiling. R-value is just one factor among many to be considered when deciding which insulation to use. Builders must also understand many other topics, including air leakage and moisture movement. No one has yet invented a ‘magic number’ that replaces the requirement for builders to study and understand building science principles.
Does radiant heat pass through insulation like radio waves?
Another scare tactic employed by some marketers of radiant barriers is the idea that conventional insulation materials — sometimes called ‘mass insulation’ — allow radiant heat to pass right through them. Scam artists have been known to warn builders that ‘mass insulation is transparent to radiant heat.’ The implication is that a layer of aluminum foil is necessary to prevent radiant heat from traveling like radio waves right through a deep layer of cellulose.
In fact, most mass insulation products do a good job of stopping radiant heat flow. Radiant heat easily travels through air (for example, from a wood stove to nearby skin) or a vacuum (for example, from the sun to the earth). But radiant energy can’t travel through a solid material.”
Read the entirety of this article on the Green Building Advisor blogs.