Compression Force Deflection (CFD) Calculator for Foam Gaskets
Turn a data-sheet CFD value into the actual closure force your enclosure needs: F = CFD × area. With the ASTM D1056/D3574 background, a worked example, and how to read the result.
Built for: sizing latch and fastener loads, checking lid stiffness, and picking a foam firmness that seals without crushing.
CFD Closure-Force Calculator
How it works — formula, worked example & reference
Formula: F = CFD × A — closure force equals the data-sheet CFD stress at your working deflection multiplied by the compressed area. CFD is measured per ASTM D1056 / D3574; this tool takes your TDS value as input and does not assume one.
Worked example: A 2″ × 2″ foam pad (A = 4 in²) with a TDS CFD of 5 psi at 25% deflection: F = 5 × 4 = 20 lbf to hold 25% compression.
| If your assembly provides | And the gasket needs | Then |
|---|---|---|
| Less force than F | Its design deflection | Seal may not compress — reduce area, pick a softer family, or add fasteners |
| About F | Its design deflection | In the window — confirm tolerance stack |
| Much more than F | Its design deflection | Check for over-compression and compression set; consider a firmer family |
CFD values differ by family and thickness — always read them from the specific material TDS.
These results are engineering estimates for preliminary material selection; final validation is the responsibility of your engineering team.
Common questions
What is compression force deflection (CFD)?
CFD is the stress required to compress a cellular material to a stated deflection, most often 25%, measured per ASTM D1056 (sponge rubber) or ASTM D3574 (flexible foam). It is the number that tells you how hard a foam pushes back.
Is CFD the same as durometer?
No. Durometer is a surface indentation reading on solids; CFD is a bulk compression stress on cellular materials. Two foams with similar surface feel can have very different CFD values.
How do I get closure force from CFD?
Multiply the CFD stress at your working deflection by the compressed gasket area: F = CFD × A. That is what this calculator does — the CFD value itself must come from the material data sheet at your actual deflection.
What compression should a foam gasket run at?
Typical design windows for cellular gaskets run roughly 20–50% deflection depending on family. Below the window the seal may leak; far above it the material can take compression set. Check the family data sheet window.