Testing Layered Composite Materials of Significantly Different Permeabilities

All of the tests below were performed on the same specimen by the same individual on the same instrument (Frazier Air Permeability Tester) at 0.5 inches of pressure drop.

The specimen consisted of a 3 layer composite material made up of a "resistive layer" (approx 0.040")(low air permeability) adhered tightly between a cap (face) layer (approx 0.200") and a padding layer (approx 0.460").

The overall approximate noncompressed thickness is 0.700"

Padding Side

Face Side

The major issue faced when testing composite materials using the standard clamp is edge leakage. The results shown in the table below show that when using the USH-1 there is little difference which side of composite specimen is up and which is down. Edge leakage is virtually eliminated using the USH-1.

With the standard clamp set at different pressures, it can be seen that the side that is up makes a significant difference in the reading. The Cap (face) Layer compresses the least so that when this layer is down, more air enters through the edge of the composite. The Standard Clamp with ring reduces the edge leakage but has no rubber seal between clamp and ring. The USH-1 with Insert virtually eliminates the edge leakage so that the differences in permeability at different amounts of specimen compression depend upon the amount of compression to the edges of the material that reside within the specimen test area.

As it can be seen with the differing results below, when testing composite materials it is important to detail the clamping procedures when reporting test results. Example: Sample #9 tested at 0.5" pressure drop; face down; using USH-1 with 0.200" thick insert completely compressed with 12 lbs of weight.

Air Permeability Testing of Composite Materials
Clamping Procedure Face up or Face Down Airflow in ft/min Airflow in cm/sec
Standard Clamp compressed to 0.200"
face down
8.88
4.51
Standard Clamp compressed to 0.200"
face up
3.87
1.96
Standard Clamp compressed to 0.175"
face down
6.01
3.05
Standard Clamp compressed to 0.175"
face up
3.05
1.55
Standard Clamp compressed to 0.300"
face down
18.10
9.19
Standard Clamp compressed to 0.300"
face up
9.35
4.75
Standard Clamp w/ 0.200" ring
face down
5.09
2.58

Standard Clamp w/ 0.200" ring
face up
4.89
2.48
USH-1 w/ 0.200" insert & 12 lb weight
face down
5.37
2.73

USH-1 w/ 0.200" insert & 12 lb weight
face up
5.27
2.68
USH-1 w/ 0.300" insert & 12 lb weight
face down
13.33
6.77
USH-1 w/ 0.300" insert & 12 lb weight
face up
13.29
6.75

Original MS Excel Results Data File