Non-hardening adhesive

I am wondering if any of you know about glue/adhesives that do not harden over time after they are applied or glue/adhesives that take a really long time to harden after application. I need the glue to temporarily hold polymer sheets before they are sewed together.




I think you could use some types of [Butylrubber](http://en.wikipedia.org/wiki/Butyl_rubber). If I'm not wrong from Isobutylene is derived the Post-it adhesive. However you can find Butyl tape easily in every big hardware store (especially nautical) or online.


EDIT
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At this [link](http://www.exxonmobilchemical.com/Chem-English/yourindustry/butyl-rubber-applications-adhesives.aspx?ln=productsservices) you can find some more information this is an excerpt:



> 
> Tapes and flooring adhesives Exxon butyl rubber can be used in
> adhesive formulations for transparent tape, hot-melt pressure
> sensitive adhesives, mastic for pipe wrap tape and vinyl floor tile
> adhesives. It can also be used for semiconducting electrical splicing
> tape. A rubber splicing tape must be self-fusing; i.e., when wrapped
> upon itself, it must fuse to the underlying layer, forming a permanent
> bond. The self-fusing is a result of compounding and eliminates the
> need for application of a separate adhesive coat. These compounds have
> very high tensile strengths and exhibit some degree of recovery or
> elasticity. Electrical splicing tapes based on Exxon butyl rubber have
> moisture resistance, outstanding aging resistance and good electrical
> properties. Polyisobutylene elastomers have long been successfully
> used in pressure sensitive adhesives both as primary elastomers and as
> tackifiers and modifiers. Exxon chlorobutyl rubber can be used alone
> or in blends with other polymers to achieve special properties in
> pressure sensitive adhesives.
> 
> 
> 


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