Low-cost Interior (Secondary) Windows for Soundproofing and reducing sound passing through existing windows.


For maximum sound reduction, the plastic acrylic panels should be thick and heavy, at least 1/4″ thick.  They should be readily removable.  They should not yellow from UV (Ultra Violet) sun rays over time.  They should be relatively inexpensive to buy and make.  They must fit well to eliminate sound leaks.

To overcome these and other shortcomings and still be able to have a reasonably cost effective product, we introduce:

MAGNETSEAL FRAMING for acrylic panels..

Start by taking your window measurements top, bottom and sides – for the plastic panel you need. (Which you can obtain locally from any plastics outlet.  (Look in the Yellow Pages under Plastic Suppliers). Have them cut your plastic 1/4″ or 3/8″ thick panel to size.  You need to decide whether to fit the flat sheet inside the edge frame of your window or over the face of the frame.  We recommend fitting over the entire wall opening because it will give a little more dead air space, which is what makes these types of windows work so well. Fitting to the inside opening may be more difficult than you imagine, especially if the opening is not square.  Only an inch or so oversize  of the opening is needed.

Take your acrylic edge measurements and add them together to order enough steel “Mounting Frame” and our special “peel off adhesive backed” 1″ wide Magnetic Tape for the job.  To install a 1/4″ or 3/8″ acrylic (Plexiglas) panel in your window you will need 4 “L” shaped metal trim pieces and enough magnetic tape for attachment to around the edges of your acrylic panels.  The  trim and the tape are sold by the foot, so you only have to buy what you need.

Window Magnet Seal

To install your window: Flush or Recessed?

Apply tape tape strips all around the acrylic edges as shown.

Attach the “L” shaped metal mounting trim to the window frame edges using screws, double sided tape or adhesive – if the new window is wider and taller and to be mounted over the face of the  opening, attach the trim angle over and around, covering the entire frame opening.


If Recessed, (This is harder to do) attach with the one leg of the “L” facing toward the existing window, just recessed enough for the new plastic panel to be  flush with the opening frame as shown.


Magna-Seal Magna-Seal Window


  • Make sure the magnetic tape does not have any gaps in the butt edges where it mates with other strips of tape at the corners.  These gaps will leak sound.
  • See that your “L” shaped trim is flat and square (not twisted or distorted) with the magnetic tape for maximum attachment strength.  Caulk the corners if there is any gap. The “L” trim goes around the entire perimeter of the window frame, not just in the corners as is shown for clarity in the drawings. If your windows has a “sill” to support the new window pane, you’ll not need tape and “L” channet for the bottom edge.  If no sill a few pane support screws should be added to prevent the pane from sliding down.
  • If there are any gaps that could leak sound, fill with caulk.
  • To quickly remove a flush window, use a bit of sticky tape.

Notes: If you desire a window that will not yellow or pass UV in the very long term, ask for Museum grade acrylic.  It will not yellow or pass UV for 20 years or more.  (Regular acrylic will last 7- 10 or more years, depending on climate and UV present).  Another of the advantages of using acrylic is that you can get it with tinting!

It’s best not to use polycarbonate or Lexan because it’s unbreakable and may delay in an emergency.

Tips on your existing windows: They must not pass any air through any gaps or crevices. Caulk or otherwise seal them off.  If need be, use some of our black foam, closed cell tape to make a gasket where they close.

If you have steel frames, (not aluminum!), you can use the magnetic tape without buying our metal framing stock. The plastic sheet will have to fit over and on the face on your frame.  If you want to mount this way, you don’t need the “L” frame, just use the magnetic tape, but you may not have much  essential air space.

You’ll need the small screws we supply to attach the L” shaped metal mounting frame, use the sheet metal type to attach to a metal frame (You’ll need to drill small pilot holes), and the supplied wood screws if PVC or wood.  Construction adhesive can also be used.  Double sided tape could be used with a small window, depending on the durability of the tape.  Do not attach the “L”  with the screws on the face where the plastic sheet goes!

* Why not just use glass?  Of course glass can be used and may even be cheaper.  But consider this:

The chance of breakage is far greater when installing and especially when removing the panes from the frame for cleaning, etc.  For this reason, use safety glass as it has a plastic center/filler which reduces (but doesn’t eliminate) the hazard of shatter and splinter effect if broken.  If it falls out and breaks, it will be finished – not like plastic. 

* IMPORTANT:  Keep the heat build-up in mind in the windows airspace that might occur if the window is facing the sun- your blinds, curtain, etc may get fried if they are inside the enclosure.  Window tint on the existing window might be in order if that could be an issue.

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