Originally Posted by squirreltrench
Also, the knowledgeable folks around here say to create an air gap behind the trap. An airgap equal to the depth of the trap almost doubles the trap's effectiveness.
No, the knowledgeable say " it depends on the material's air flow resistivity" With SNS going solid up to three layers is best bang per volume and buck. 4 is iffy, five or more total layers thickness use 4 layers and and the rest airgap.